My 87 has a really rough idle when you first start it up, to the point that you have to keep giving it gas to keep it from stalling. Once it gets to closed loop it improves dramatically and will eventually settle at 700-800 rpm. Runs great on the road, and will continue to idle smooth at red lights or when returning home.

Previous owner removed the cats, but I don't think made any other changes. She does burn some oil (pretty sure it needs valve seals). Oil pressure is good though, engine temp is right around 200F.

I did notice a little fluid on the intake manifold this evening under the throttle body by the thermostat housing, pretty sure it's coolant.

She will throw a code 32 for the EGR occasionally on the highway once it's well warmed up.

That's about all I have observed at this point in the couple of weeks I've owned it.

 

You need to take a look at your coolant sensor. You engine thinks that is warm when it is cold. You are getting a lean condition, hence the "feathering" of the gas you need to do to keep it running and once warm the car runs well. These are the classic symptoms.

Swap your sensor and I bet the code 32 goes away as well.

 

Engine basically reads TPS voltage and Coolant temperature to set its parameters for open loop running.

I'd check with a scanner to see what the voltage reading was (should be about 0.54V) and if its holding steady or varying wildly, and what the CTS is telling the computer.

I wouldn't give any thought to the Code 32.

 

I would check to see what the ECM sees for a temperature with an infra red thermometer and while I am at it. See what the scanner says the TPS is. Perhaps dirty IAC?

 

I'm sure this has been covered, but what does everybody use for a scanner on these older cars?

 

I use an Actron that you can get at Advance that reads OBD1 cars for most daily stuff.

I use the laptop with DataMaster to troubleshoot other problems.

 

New CTS seems to have made no difference. Emissions are strong when cold, cats are removed though. Still need to feather the throttle, then once it hits closed loop it starts hunting between 500 and 1100 rpm. I took it for a drive, got back, temp about 200F, and idle is pretty stable.

not throwing any codes per the paper clip method.

 

I still need to pick up a scan tool, but I'm leaning towards the IAC. I was going to pull the throttle body for a good cleaning. Are there any tests I should run first on the IAC? I will probably replace it since I'm going to have the throttle body off, not terribly expensive, but I'd hate to get everything back together and end up having to replace it.

 

I wouldn't for 2 reasons. First of all, it is a bad habit to start. Throwing parts at a problem is why people are suspicious about EFI as far as reliability. Second, you'll introduce a new variable. They can be bad out of the box.

Paper clip is worth what you paid for it. Your ECM isn't that sophisticated. It has to be far out before a code is thrown.

 

How is everybody reading sensor voltages, real-time scanner? I see Obd1 code readers, but what's a good real-time scanner?

 

I have a Snap On MT2500 i picked up from ebay. You just have to make sure it comes with a GM1 connector and the correct year cartridges for your 87.

Gary

 

I do. MT2500 or auto x-ray

 

I pulled the throttle body and gave it a good cleaning focusing on the IAC. Put it back together, reset the IAC and fired it up. Open loop idle appears to have improved, races up to about 1100 for a few seconds then settles at about 700. Once it goes closed loop though, it's still hunting around. Test drive went well.

So I'm guessing the IAC is the culprit, good cleaning caused major improvement, but still not perfect. is it possible the old ISC is still not functioning 100% and should be replaced?

 

Did you get new gaskets put on? Did you set it according to the tach or scanner?

 

Been a while, but here is my latest:

went through a can of worms cooling system service, but while I had everything out I decided to rebuild the throttle body, new gaskets and replaced the IAC since I had it apart. Buttoned everything back up tried to start it, wouldn't but realized I forgot to reset the IAC.

performed IAC reset with a paper clip in diagnostic mode, disconnected sensor, then turned car off and removed clip. Reconnected IAC, started right up and settled at 600 rpm. Was looking like my open loop issue was resolved. When temp was about 137 I tried to give it a touch of throttle at the TB, because I was in the process of bleeding the cooling system. As soon as I touched the throttle it stalled and wouldn't start again. Not sure if it got to closed loop prior to stalling or not.

So, I was focused more on the coolant level, but in hindsight it might have started running a little different prior to stalling, can't say for sure though.

The last time I drove it prior to this job I had two instances where I noticed a hesitation when hitting the gas. Im running the level down to get ready for a filter service, about 1/8 tank give or take.

im thinking maybe a fuel delivery issue, that's next to check, but just seems too easy with my luck. Any thoughts on where else to look? I was going to study the FSM tonight.

 

One last detail, no check engine codes.

 

How did you ascertain 600 rpm? Are you sure there were no air leaks that the ECM was compensating for? ECT?

Could be spark. Have you checked for weak spark and wire leakage? Have you checked fuel pressure and see what it takes, time wise, to bleed down? What is fuel pressure at WOT? Your reset procedure depends on everything being spot on except the IAC setting. That is why I don't like to use that method.

 

600 rpm was the tach reading while idling.

im sure it has vacuum leaks, I'm working on that in parallel. It was running ok prior to the throttle body fix, although I have removed the throttle body and IAC before without issue.

I need to check fuel pressure still. I did get it started this morning, but it was a hard start and it would stall quickly. I tried to disconnect the MAF per the FSM, but no change so I don't think that's the issue.

 

1. if you know you have vac leaks, you need to deal with them or you are asking the computer to compensate. which it will to an extent but to dial in all your issues you need to take care of the ones you know exists.


2. can you confirm that after you installed the tb, you carried out a minimum idle set procedure? aklims method of observing the iac position while setting the tb set screw is by far the best, in the absence of tha real time scanner, follow the manuals method. but u need to at least deal with the known vac leaks.

 

I'm assuming there are vacuum leaks, but I don't know for sure, still working through that.

Looking at the idle set procedure in the FSM, it sounds like it wants the engine started while in diagnostic mode after disconnecting the IAC before setting the idle to 450 rpm. I didn't think you could do that without damaging the ecm.