I got an 86'coupe that runs great, the question is oes the ECM control the idle?(let me explain). I can start the car and it will idle up like its suppose to then it will finally settle down to 700 rpms at WOT, but if I shut the car off and restart it, it takes about two minutes to go from 1,000 rpms down to 700 rpms. and also if I come to a stop. It will take a minute to idle down to the normal 700 rpm again . so i ask again, Is the idle controlled by the ECM at WOT?? or is it in the throttle body??? Thanx. Anyone???

 

hold on, 10,000 rpm? it can not rev that high.. do you mean 1000? please re explain what it is doing

 

ECM controls idle via the idle air control valve, all the time.
Proper minimum idle setting and throttle position setting, are required for the ECM to control idle to the best of it's abilities.

 

If you do have an IAC [ Idle Air Control Valve ] and have had occasion to unplug it it might need to be reset.
Check the FSM for yours but the later models go like this.
Unplug IAC connector [ under throttle body ] and start engine.
Run for a minute or two then turn off switch. plug connector in and turn on switch for a minute then turn off . Restart engine and see if it does better.
You might want to take it off and check it for carbon or gunk next.

 

Restart engine and see if it does better.
You might want to take it off and check it for carbon or gunk next.

If that doesn't get it, remove the throttle body (TB) and get an old toothbrush and a large plastic bowl to set it in. Get a can of aerosol TB cleaner, some shop towels, and go to work.

Also, remove the IAC motor pintle and using a shot of aerosol IAC cleaner, remove any carbon that's fouling the pintle spring.

Do this once a year. It really mellows your base idle and improves throttle response.

 

Except for the length of time it takes to return to a normal idle upon restart, the restart is normal. And the coming to a stop, wherein the ECM gradually reduces idle to keep it from stalling (like a dashpot on a carb) is somewhat normal.

When you turn it off, the ECM retracts the IAC pintle to allow more air through the throttle body for a quick restart. The published spec is about a minute before it returns to it's usual idle - so you might want to watch the second hand on your watch and see what it does. If it is 2 minutes, scan it and see what the ECM is commanding for Targeted Idle, Actual Idle, IAC counts (the more there are, the faster the idle) and TPS (which is a voltage signal representing the position of the Butterfly). Whatever the TPS voltage signal is when it's idling right, it should return to immediately the moment you take your foot off it. Assuming everything is right but it isn't responding to what the ECM commands, there's either a bunch of crud in the throttle body or IAC pintle/passageway; the IAC motor has weak coils, or there's an air leak somewhere on the throttle body or possibly a small vacuum leak that it needs to compensate for. If you do find that the TPS isn't returning to idle voltage then you should ckeck the throttle linkage and the Butterfly to make sure something isn't hanging it up. If you fix what it's doing on restart, then it should also fix what's happening when you pull up to a stoplight.

 

I will check for trouble codes to see if you have a open loop in the EGR valve it is common problem and also check the O2 sensor, the ECM which control the idle maybe mislead by these components. Check your timing follow the instructions at the radiator shroud. Check your base idle and IAC for proper settings and if you have catalyst converter check for clogs.

 

Thanks everyone that responded( and yes I did mean 1000 rpms instead of 10,000 rpms. senior moment I guess LOL by the way, I did have the throttle body off last season and it was pretty dirty inside, also there was some carbon buildup on the IAC shaft . it did idle much better after I cleaned out the throttle body and I replaced the mounting gasket and the IAC gasket, so i would say that my next step is to replace the IAC and see what happens?

 

Have you tried to set the minimum idle and TPS. If your min idle setting is out of whack, it could result in idle problems. The TPS has to be re calibrated, anytime the min idle screw is adjusted.

 

Yes , I already readjusted the base Idle and reset the TPS

 

What do you mean by later models? Will this work on my '90?

 

When did you do this? Also what are your IAC counts at idle in closed loop? Should be around 20 counts. What is your TPS set to?

 

i reset it after it began to idle ruff and was surging, the TPS was readjusted to .54 volts. I dont have a scan tool , how can I tell what count if I dont have one??

 

Can you borrow one? Maybe an autozoo?