I read through the forum and didn't see the symptons I've experienced, so here it goes.

Starts great, on the tac - cold the idle jumps to 9 as it warms up it goes down to 6.

It will be idling fine then it jumps up to 8 then back down to 5, then back to 6

Then at one point it went down to 2 and like hiccupped and then back up to 6.

Thats the pattern during idle.

It hasn't stalled and when I'm cruising along it seems fine. There are no codes. I just cleaned the MAF and replaced the relays.

Hope this makes sense.
Thanks
Robin

 

Mine has been doing this exact thing for a while, but something that seemed to make a difference was new injectors.

 

Try a can of Seafoam engine treatment.
Put 1/2 the can in through your brake booster vacuum hose and the other half into your fuel tank. Good Luck !!

 

Could be the IAC or TPS (or some other things). Mine idles a little rough cold since I changed injectors, runs fine in closed loop.

 

Hi.
I had the same on my 85 4+3. When the engine jumps in rpm on idle it is especally 2 things that are suspicious. The most probably vacuum leakage and EGR valve.
Before going on themcheck the tube from the MAF to the throttlebody for cracks. That can be fixed temporarilly with some silicon.
Then clean the throttlebody which will have a lot of carbon deposite.
If it still is aneven idle check all possible vacuum hoses and do not forget the one going to the brakebooster.
Underneith the plenum there are some stiff black plastic vacuum tubes. These are extremely brittle and can break easily.
Check for vacuum leaks around the runners where they enter the manifold by spraying propane or starting gas when the engine runs. If the rpm increases there is a leak.
Then there is the EGR valve. There is a vacuum input, If you have a vacuum pump. Apply vacuum and see how long the vacuum holds. It should hold about 20 seconds. I this is ok there might be some carbon deposites on the vale seat or pintle and this must be taken away. It is said that it is possible to see the pintle move through an opening but havent tried tolook after myself as mine had a bad vacuum membrane .
If the idle is better after rinsing and repairing the broken hoses or even if it is not better it might be the vacuum toriod (control valve whic is controlled by the ecm on right side of the plenum by the firewall).
Check the TPS voltage by measuring the two upper wires and it should be .54V up to .63V . =.54V is nominal voltage. Check for minimum idle air adjustment. There is a procedure on the forum I think or in Helms but be sure that you disconnect the ignition spark timing cable a brown/black cable at the brake booster to ensure the ecm do not try to compensat the rpms during the adjustment.

For me it was EGR, vacuumleak and the min idle air adjustment.

Good luck

 

ECM provides fuel based on Load and Coolant Temp and has a Targeted Idle that it maintains with the Idle Air Control Motor. Something is telling it that it needs more, then less. That can be a funky a/c signal or an air or vacuum leak beyond the MAF or even a bad MAF and a couple of other things. I'd hook up a Scanner to see what's taking place, but try it with the MAF disconnected and then with a/c on/off. Also try clamping off the fuel emissions hose from the Charcoal Canister to the Throttle Body; then the Air pump hoses at the Headers. Finally take a look at the #7 plug and compare it to the number 6 checking for rust on the threads or a clean electrode which would indicate that it's sucking coolant. That leans out that cylinder and the ECM dumps fuel.

 

Have you taken off the TB and the IAC housing and cleaned it recently?

 

I cleaned the TB yesterday, man it was dirty. Cleaned the MAF and noticed it was missing the seal towards the air filter end. Ordered that. I did notice after cleaning the TB the idle is fairly rock solid at 6. After a couple of minutes it dips to 5 for a split second then jumps to 7 for another split second before dropping back to 6. I know thats the computer compensating for whatever isn't right. So I'll be getting IAC cleaned and will have the car checked for vaccum leaks. Need to replace fuel filter, which I have.

I also sea foam treated, but the oil.

 

When you clean the IAC, you have to take the IAC out and the IAC housing off which is part of cleaning the TB.

Waste of money. If your car has stock injectors or have not ever cleaned them, this would be a good time to do so. Your SOTP dyno cannot tell if the injectors are spraying properly or not. And no, the Ohm test doesn't do that either.