1988 5.0 Rough Idle Hesitation after start

[The Needs Of The Many]

Hello. I have an 88 Ford Thunderbird with a 5.0 engine. Forgive me, but...what is the RPM supposed to be in PARK and DRIVE? Is the only adjustment the single screw on the throttle body? In park, the car idles fine. Put it in drive after either a cold/hot start, the RPMs drop slowly and the car runs rough for about 30 seconds then I suspect the computer clears up the problem as it runs fine and smooth. ORDERED the Hayes repair manual and it does not have Tune-up specs only how to repair the engine or rebuild it. The car also hesitates when it runs rough but stops hesitating after the computer "adjusts" the rough idle. In California and worried about smog testing. Most mechanics where I live won't work on OBD1 vehicles. Any advise will help. Thanks in advance. Oh, and...EGR, EGR position sensor and solenoid have been replaced.

 

[74 Harley]

You idle is entirely controlled by the computer. You need a reader that's compatible with OBD1 systems.
There's no real "tune up" on these cars. Just cap rotor and wires, occasionally spark plugs.
It sounds like you have a small vacuum leak. Does your check engine light come on?
Have any of the emission controls been eliminated or tampered with?
What part of California are you in?

 

[The Needs Of The Many]

Thanks for your reply. So Cal- Azusa is the city. The EGR valve, solenoid, and position sensor was replaced BECAUSE when I disconnected the vacuum hose the bucking stalling stopped. Changing them did no change to condition unless again I golf teed that vacuum hose to the diaphragm. I was thinking IAC because even though I cleaned it, the problem remained. Even the TPS was entertained, and my voltage to it is .98. PCM makes sense...it is the one that lowers idle and after rough running it corrects the problem. Due to lengthy time to "self adjust" the issue, I fear it will fail smog.

 

[74 Harley]

Those little idle control motors are a pain. I replaced many of them. I never had good luck with cleaning them.

 

[Tom Alpers]

As others have said, those IAC gizmos are hard to clean. Many times they were worse after I cleaned them. Best is to buy a new one. Also, as to the rough idle.. I had that engine in an 88 mustang and replaced all the fuel injectors because of rough idle and that made a huge difference.

 

[The Needs Of The Many]

Thank You, gentlemen, and I do have one last question: When I disconnect the hose to the diaphragm on the EGR valve, the UFO-looking thing, the car does not hesitate and runs correctly. However, the RPM does lower but it does not affect the performance of the vehicle; no hesitation or lean-out issue causing rough idle. I did not want to keep the EGR disconnected and plugged with a gold tee for fear of valve damage, as I had read that this can increase piston chamber temps and that the vehicle was made to work with the EGR system, and not to "EGR delete" like some Mustang owners with the electronic plug and the plate. However, when it is connected I do notice the diaphragm on the EGR moving in and out when I give it the throttle. I might have done a better job cleaning the EGR ports, as I used carb cleaner and a toothbrush- but I heard you have to use a brass type brush to scrape away the carbon, not a toothbrush. I did look inside the throttle body from the butterfly and noticed a ring of black around the port where the EGR enters the throttle body. Question: one port from the EGR on the TB goes directly into the TB. The other port, which I could barely see, sort of twisted and turned and did not lead directly into the TB like the other. Where does this port go? What does this port do? Can I still clean it on the car or do I have to remove it/replace it? Your input here is greatly appreciated. 1. Can I run the vehicle with EGR disconnected until I can repair it? 2. What does the other EGR port do flow through that does not go back into TB? Thanks, you guys are the best.

 

[74 Harley]

Yes the design of the egr is to help lower combustion chamber temps. You will not harm anything by plugging it.
May I suggest that you find a vacuum hose routing diagram and chase down all of your hoses.
If I remember correctly the egr vacuum should go through a thermal port sensor, not directly off the manifold, as the egr valve is only supposed to open at set times. (Think highway cruising and off throttle). It's not supposed to open at idle.

 

[74 Harley]

Had another thought, you have 2 hoses on the egr? Swap them. Worst thing that can happen is you have to put it back...