1994 start-up idle problem | Ford Thunderbird forum club group 1955-2005 models

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1994 start-up idle problem

  • Thread starter Thread starter Pearl 94
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Pearl 94

Pearl 94

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1994
Recently, my car will not idle when I first start it. Sometimes will stumble, and than idle roughly, most times will die. Step on the gas pedal to stop the rough idle, and it dies. I can override the problem with the two-foot gas/brake method, bring the rpm up to throttle body opening, put it in gear and away I go. After a minute or two, it will idle when stopping at a light or similar.
My bible-size maintenance manual says the idle is controlled by the IAC, idle air control valve. Got a new one of those, put it in and no change. More reading, the power control module controls all the fuel functions, idle, acceleration, etc.,. Read up and tried the PCM reset options. Before I go and find a new/repaired PCM, I am wondering if that is the problem. Other than the starting problem, the rest of the car works well, Acceleration, gear-shifing etc. I do have an older-style OBD reader, but it shows no codes. It seems as though one of the inputs to the PCM needs to "warm up" or stabilize to enable the idle function. When the engine is warmed up, it idles smoothely, and accelerates smoothly, so I am pretty sure it is not a fuel delivery or injector problem.
FYI: I may have caused the problem inadvertently: I had the battery disconnected for 3 or 4 hours when I had the dash out, to replace the small gears in the odometer. Found out later, that when the battery is disconnected for a long period of time, many of the electronic modules, including the PCM lose the stored information, and have to "re-learn" inputs when the battery is re-connected. As i said, I have tried 2 or 3 times to do the recommended reset but didn't help.

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Is it a 4.6L ?, if so, it sounds a lot like what I went thru years ago, rough idle when I crank up cold, then smooths out after a few minutes, ran fine other wise, I first tried a IAC, no change, got a used PCM off ebay, no more problem, runs like new..................
 
In the old carb days what you describe is exactly what happens when the old choke systems didn't enrich the cold mixture enough on start up. Rough idle, feathering the gas pedal, etc. I think you might have a lean mixture.
Why ? I can't say...
 
Thanks for the replies, guys. As for replacing the PCM, I think that is what it will take. have looked on line, and they are available. As for a lean mixture, i don't kinow about that. 2 or 3 times when I start the car and have the window open, I can smell gas, so i am wondering if it is a too-rich problem rather than too-lean? Obviously, as it is fuel injected, the smell would not come from the engine, but from the exhaust.
 
First off the scent of fuel is normal when it is cold, I smell that on mine sometimes, that's just the PCM pouring in a ton of fuel, that's why stone cold you can drop it in gear and take off down the road like it's all warmed up already.........remember the PCM is setting the air/rich mixture........I'd still consider a used PCM, the car is over 30 y/o, mine is a '95 and I started having starting issues and random roughness during some cold starts, never that once it's warmed up.......If you looked into those PCM's on ebay you probably saw between $60. and $150........Now shouting at the PCM, we are assuming that all the sensors are giving the PCM a proper signal and the PCM is passing back incorrect info to motor as to how to adjust......One more thing, a failing PCM always seems to give ya bad fuel mileage, not super bad but you'll think ya should be getting better..............Oh, when ya pull that PCM, make sure ya buy one that has the correct catchcode, mine was A5WO, that code has to match or you'll have a low idle and it will not shift right........hope all this helps.....
 
Oh, ya never said anything about codes, have ya checked to see what codes ya got if any? now my failing PCM never gave me a PCM code but it was giving codes that was not there........one other thing a mass air sensor could give you the issues that you describe also, consider how long has it been since the mass air sensor been cleaned or replaced...........just a thought.....................
 
In a bit of a quandry at the monent. looked (again) at the Tbird/cougar electrical troubleshooting manual and it shows the PCM connector to be one large 104 pin unit.
All the parts dealers as well as PCMs for sale, show two connectors 8 double rows each side. That's the easy part. I thought I would pull off the right side kick panel (where the module is supposed to be!) and see if there were any part numbers or such, to relate to replacement module. Pulled the kick panel off and the insulating panel behind it, to find no square PC module. Only small block connectors and wires. Just above the kick panel, right under the dash, is a "module" that would appear to be the PCM. 2 screws on a metal plate bolted to the module. It has two plugs, 6 pin connections on one side and 8 pin connections on the other. The 6 pin side is full, the 8 pin side only uses the inner 6 pin slots. No marking on the module other than FORD. So. Have I found the PCM or is it some other module?
Thinking of a possible cause, as I said, it seems when the idle smoothes out, it is after running for at least a minute as though it takes something time to warm up . With that in mind, I see that the PCM has inputs from 4 heated oxygen sensors. If one of those was bad, it would mke a convenient reason for the rough idle.
Re the question of codes, no - I have checked two or three times and there are no codes., but as I said my OBD reader is like me, old!! Might not be able to pick up the more modern in/outputs.
Hadn't thought about the Mass flow sensor, will have a look at it.
 
Yes the pcm has one very large 100+ pin plug in only the modern cars/trucks have like 3 plug-ins going to it, now like I said if your '94 is like my '95 that pcm will be behind that right kick panel under a couple layers of plastic as you described, and yes, there is many white-squared plug-ins around that pcm, my guess is that you were looking right at it and could'nt find, I did this also, in that kick panel area kinda look toward the center left to find that massive plug-in, there's one hold down hex-bolt holding it down just on the right side of the pcm, I'm pretty sure it was a 10mm size and I remember where this hex head is it is in a white plastic area, now probably what your missing is that you can only see the plug-in and only about the bottom third of the pcm, it's tucked up higher than you think and I'm pretty sure that the printed side of the label on the pcm is facing you as it's mounted in, now I also need to say that I had trouble mounting mine back in because the plug-in needed another 1 inch of wire to plug back in, I tried but only ended up bending 4 pins, after fixing those pins, I now run with the pcm on the passenger floor board............When you get that out and start matching it to what's on ebay, concern yourself first with the 4-digit catchcode, second the part number, all these mn-12's have the same part # but the last 2 letters and thats a biggie, my catchcode was A5WO (printed in dark black)and the last 2 letters on my part # was CA..........
Now you still never told me if this is a V8, and as far as o2 sensor, they are most likely to give a code and give an issue all the time rather than just during random cold start, I'm still leaning toward pcm in your case..............
Don't worry about a cheap code reader, I know they have some fancy one's today for big bucks but I've been using a $12 dollar one for many years and seems to be working just fine..............
Let me know how it goes, and keep in mind that I can only post 3 times every 24 hrs, I'm not a paying member.............
 
Will have anotherlook at the kick panel area to find the PCM. And the car is the LX coupe with the 4.6 V8.
Reply to Alex: thanks for your input, but all your replies are in Dutch, and i cannot read them!
 
O,i am sorry for that,i think you must first measere your battery with a voltmeter when the tension in cold condition is lower than 12 volt don't works as it must, when the engine runs for a wile is it over.....it is a possibilety,sorry for my langueats mistakes,succes...Alex
 
Alex: battery voltage is good, everything is good except the rough idle. I am, like mcm51 suspecting the PCM
mcm51: had another look at the kick panel, and as you said, I wasn't looking high enough. Saw the connector with the bolt that holds it in, and the module above. There is another insulating baffle over the lot, and although I can wiggle it a bit, cannot pull it out. Might have to use some tin snips and destroy it!
However - While it will be a bitch to get the securing bolt out and the plug down from the module, I cannot see (at this point) where the module is bolted. I dropped the glove box thinking I could get some access from there, I can see the module, but again cannot get near it. I have a friend who has a new high-dollar OBD reader. I will see him and try and verify that the PCM is bad and I can get a suitable replacement before I dismantle half the car to change it!
Thanks for everybody's help. Will let you know how things progress.
 
yea, I knew you would find that pcm, and yes, that's the first thing I spotted when I went at mine was that massive plug-in, I never had a problem getting mine out, that one hex head bolt to the right of the module, take that 10mm hold down bolt all the way out, then slide module down, I don't think I went to un-plug it till I had it out of the holder once I removed hold down bolt, mine slide down real easy...........I'll be interested in what catchcode you have and what the last two letters are on that part #........ And I'm sorry, I should have told you that this swap out has to be done with the glove box door flopping, seat all the way back, lay on your left side, right hand/arm reaching through glove box door opening..........
The problem with checking for codes now is that you just had the battery un-done, it's probably clear of any codes, and most important to keep in mind is when my pcm was failing, this went on for a least two years randomly and I not once ever got a pcm code, so don't bet that you'll get a code, I did'nt............
 
Won't be able to have the PCM checked with the "newer" diagnostic tool until Tuesday. But in the meantime, After the last reset yesterday, the idle starting problem is better, and when the engine is warrm it runs great, acceleration is good, and idles very smoothly, so the injectors, fuel delivery etc. are good. The catchcode is E4A3, and the last two letters on the p/n# are AD. In preparation for maybe getting a replacement module, saw on line, a site called Flagship One, who lists the part number identical to mine, and who will (after sending the VIN) program the module to the original specs. So that is an option.
As for actually replacing the module, being old and not so flexible anymore, I looked at and think I will take the passenger seat out, to give me more room to get at the module.
 
Interesting, E4A3, don't recall that one but do recall a part # that ended in AD, I was kinda hoping you had a A5WO, they seemed pretty common, I'm not wild about flagship one, one of the 5 or 6 pcm's I tried on mine, yes they took my vin and sent me a catchcode H5TO and I questioned them when I received it, they said it would be ok, It gave me a real low idle(500 in park,400 in gear and never a high idle even when cold), and I thought it did'nt shift that great, ok but not like it should, I was hoping that you had my catchcode, there's plenty on ebay, maybe flagship will be different for you with the E4A3 catchcode..........Recently I've been trying to get a couple pcm's to have for future use, along the way I even tried a brand new reman from o'reilly, no catchcode on that one, it just matched my part #, that one started me right up, fast idle and all, took it out for test drive and had no 3rd gear, right now i've got the o.e.m. one with the random no-start issue, the one I'm running on now from kansas, runs great and my last purchase from swan auto Tyler, Tx. and it works great too, they said they had a bunch of mine, maybe you should consider getting in touch with them on a E4A3 catchcode...........
 
Hi again people
Update: I didn't think the PCM was totally faulty, as every other function was working fine, only the lidle problem. Tried everything I could , new thermostat (did help, got the running temp up to "normal" faster), new plugs and wires. Mild improvement. Then it got weird. Took it through a car wash with the underbody spray, and from that point it started to misfire. Not consrtant, but intermittent. It would 'flutter miss' on acceleration, and then smooth out when the rpm was held steady. Suggestions that there was a clogged or faulty injector(s), added a can of gas treatment, and also a can of oil treatment. Also seemed to help, but still mis-fired at idle and on acceleration.
The PCM I ordered from Flagship 1 had arrived, it was programmed to the model number of my existing PCM and the catchcode was the same as my original, E4A3, so I got at it and changed the PCM. Wasn't quite as difficult as I had imagined. I removed the glove box and the passenger seat. Being able to lay down flat and get both arms/hands to do the work, made it much easier.
Started the car, let it idle for about 10 minutes , (water up to operating temp, as per "re-setting" recommendations) and the car idled very smoothly, no mis-fires, about 700rpm in park. Took it for a short spin around the complex where I live, (weather went to crap here, was snowing/raining/sleeting) so didn't go far.
Today, weather is better, cold, but roads are dry, so went on a longer test run. Other than stumbling once on start-up (which I attribute to the very cold weather and the PCM not being fully programmed with all the necessary parameters, it ran perfect. No mis-fires, acceleration good, shifting good, so I am happy with the result.
Cheers and thanks to all who replied and offered suggestions.
 
Glad to hear that flagship one sent you the same catchcode as the oem one, they sent me a different one, that pcm should go thru all the adjusting it needs within about 10 driving miles of driving........I always thought most of your issues was caused by the pcm, now this is always assuming that the pcm is receiving good signals from under the hood and will know what to do with those signals now.......I thought that when you got into that pcm swap, you'd find it was'nt super bad a job to do, you never mentioned if you were able to get it all back up into the holder and all, I'm still running with my pcm on the floor board, I've got my plastic pieces back in place..........Let's keep in mind that camshaft and crankshaft sensors mean alot to that pcm AND also a good working mass-air sensor during cold starts, you might want to consider a new mass-air to go with everything else you've done, not all that long ago a motorcraft reman was still available........
 
Forgot to mention in the last post that when I had the mis-fires, I put my code reader on 2 or 3 times, including the advanced, -key on engine off and key on engine run- and nothing. No codes at all, so that convinced me to change the PCM. As for getting it in and out, I could not get near the top bolt that holds the plastic holder, so I took out the lower bolt out, left the holder in place and pulled the bottom of the holder out (good thing it is plastic) from the PCM and slid the PCM down and out. Reverse to put the new one in. Needed a 1/4" long extension and universal with the 10mm socket and some tape to get the lower bolt out and back in, but did. So all is well with the installation. I checked the MAF at the start of the problems, and it was good, clean and no codes so I am pretty sure it is ok. Had heaps more snow here last night, so a few days before a longer "conditioning" drive. If it still gives problems at start will consider a new one.
 
Well, sad to say that my old Ford has momentarily beaten me. Still have the low rpm idle at start, stumbles and almost dies, but will idle, (a bit rough as long as I do not touch the accelerator), at about 400 rpm. If I put it in gear, it will die. Starts instantly again, and if I do the 2-foot thing, one foot on the gas, keep the rpm around 1,000 and the other on the brake I can back it out of the garage and drive away. 2 minutes later, if I stop it will idle ok, a bit low rpm, but doesn't die. After 2-3 minutes or 2 blocks, the car runs great. No misses, stumbling or hesitation. It accelerates fine, downshifts when necessary and runs like it should. It appears "something' needs to warm up.
This morning, when I was going to check for vacuum leaks, I started it, did a little dance on the accelerator, and it mis-fired, stumbled, and barfed a bit until i got the rpm up and cleared the stumbling. I believe it was overfueling, as it was the same effect as when you flood a carbueretered engine. and I could smell fuel. Each time I have the rough idle starting problem, if I gently press the accelerator and get the rpm up around 1,000 and hold it there there are no misses and it runs smoothly. I am aware that bringing the rpm up to 1,000 or so, drops the idle circuit and the throttle body takes over, so that is self explanatory
To recap: I have replaced the Idle air control valve, the power control module, new plugs and wires, new thermostat, new coolant temp sensor, cleaned the MAF wires with the proper cleaner.
Of the many theories for low or rough idle, aside from the IAC and the PCM, were a vacuum leak, dirty PCV valve, and low octane or dirty fuel. Put in a new tankful of premium gas, (along with a qt of fuel additive) to clean the system and injectors. Checked the vacuum - 19hg at the port under the cowl and also installed a temporary tee fitting to check the vacuum at the fuel pressure regulator. also 19hg. PCV valve is good.
So, back to the books and open to more suggestions!
 
On the low idle, since you put that pcm in, have you ever saw a 1100 or 1200 rpm on a cold start up before it calms down OR does it go straight to a 4 or 500 rpm idle ? since you put the pcm in, have you ever seen a normal idle on a warm engine, 700-750 rpm or there about ?
You said you swapped the coolant sensor, not to sound dumb but you did swap the one with two or three wires going to it and not the one with one wire going to it ?
Has the I.A.T. sensor ever been swapped ? I don't think that might be an issue, but it's there for some reason.......
Assuming that the pcm is operating correctly, I'm not sure of your maf, code or not, I'd consider swapping it out, not just the sensor but the whole assembly.......
Now on that smelling fuel, like I said, I smell fuel sometimes on a cold start myself, we should never smell that on a warm engine, but if you are getting that fuel smell each and every time you crank up cold, that sounds like pcm or maf, I tend to believe injectors either work or don't, would not just cause a problem while cold running, then straighten out...........
My suggestion is, assuming that the pcm is working correctly, I'd go at maf next, no code, after cleaning or not and remember if you swap it, go with whole assembly, not just the sensor............
 
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