car swaying at idle after long run

[gopiqpp]

My 88 Colony Park has had this problem for a while. After a 100 mile highway drive into town and idling at the first traffic light it sways, as if someone was rocking the car up and down !! If I shift into Park or Neutral the swaying stops at once. The car starts and runs perfectly otherwise. A month ago when my intake manifold leak was fixed a general tune up was performed where the TPS was replaced, new plugs and wires, PCV Valve and filter replaced, fuel filter replaced, and the IAC was cleaned.
This swaying problem was present before this tuneup, and persists now.Someone suggested that a cylinder may be misfiring but then why should it smoothen out in "P" or "N" gear?

[cld783]

First thing i'd do is check for codes...

If i had to guess, i would say it's possible the throttle stop screw is turned in too far, creating a power brake/surge effect at stoplights. It's also possible the problem is in the drive train itself...

[Heretic]

Check / clean the IAC. Idle surging up and down make it pull a little, giving the feeling that the car is moving up and down when in gear.

[1987cp]

Your engine feeling different in Park or Neutral is no surprise, as there's essentially no load on it, versus in gear, where there's a bit larger load even when idling. My idle usually goes down about 100rpm when I drop the car into gear.

That does suggest one slight possibility, that the signal from the MAP sensor might be off slightly (since vacuum drops slightly with the car in gear, and the ECM uses vacuum to anticipate fuel needs) .... my car uses a carb, but if the idle mixture is off, it'll tend to behave weirdly and sometimes even rock from side to side a bit, and I would imagine a funky MAP signal at idle in gear could lead the injection system to mimic that condition.

I suppose there's also the possibility the IAC needs replacing instead of cleaning .... or that there's still a vacuum leak somewhere.

How's the car drive otherwise? EGR working correctly? Any noticable issues at tip-in or heavy throttle or anything?

[gopiqpp]

The car behaves perfectly while driving. Very smooth. However like in most CV's and GM's here in Saudi the air pump and its connections have been removed . I guess that because our pollution standards here are not adhered to and once the pump becomes noisy as mine did it is just removed and a different size belt is used to connect the AC Compressor. The EGR is the structure that is just in front of the TPS,isnt it ? See attached pic.It had been disconnected too when I got the car and the vaccum nipple has been capped off. Is this bad ? Could this be the reason for the problem?

[gopiqpp]

First thing i'd do is check for codes...

If i had to guess, i would say it's possible the throttle stop screw is turned in too far, creating a power brake/surge effect at stoplights. It's also possible the problem is in the drive train itself...

I know that codes are important but where I stay in a remote area we dont have facilities, No Autozone or Ford Workshops- just mechanics who can replace a ball joint or an intake manifold but know very little about codes and trouble shooting.

[1987cp]

On EEC-IV, it's possible to check the codes at home or in the field with just a piece of wire. There's a plug near the big round headlight connector, and you just jump two of its terminals together and go count flashes of the Check Engine light.

[cld783]

does this happen when your not running the air conditioning?

[gopiqpp]

does this happen when your not running the air conditioning?

Actually here in Saudi with ambient temp of 45 centigrade the AC is always on so I dont know. I will drive without the AC and try today.

[gadget73]

Usually its vacuum leaks that make it do this sort of stuff. Might want to check the work done when the smog junk was removed. If those smal lvacuum lines weren't capped off completely, it might be the problem.

[gopiqpp]

Will do. How exactly will I do this ? Is it by sraying carb cleaner or something similar ?

[gadget73]

I usually just inspect the lines. If they are not capped off, thats an obvious issue, but if they look cracked, or have any other signs of damage, thats probably not a good thing. Honestly, since you have no smog junk at all on the car, I'd find the red plastic line that goes to the rear of the intake manifold, unhook it, and cap off the pipe on the manifold it connected to. That will eliminate all of that plastic junk as a possible problem.