Occasional Idle Air Control problem???

[tonybabb]

My 89 coupe, that I bought new in 89, is occasionally (once every few weeks/ months) giving me a problem. It refuses to idle and the engine stops. It will only start if I press the accelerator slightly, once it's running I have to press the accelerator a little all the time. It does this 2 - 3 times when I try to start it and then sometimes will start normally, or I just give up and drive it with the problem, the problem doesn't go away when the engine warms up, it only seems to go away when I turn it off and then start it again.

Today for example it did this when I started it, I drove about 20 miles highway and when I pulled in to the parking lot the engine stopped as soon as I lifted off the accelerator. A couple of hours later I started it again and everything was fine. I'm assuming this is electrical but have no idea where to start looking, I'd appreciate any advice.

Thanks

 

[FForward]

Did you check to see if any codes were displayed? First place to start when you have a problem!

 

[aboatguy]

Have cleaned the IAC and Throttle body. The IAC may be sticking, or the passages carboned up. If they are clean you may need a new IAC.

Mike

 

[tonybabb]

getting code 36

Did you check to see if any codes were displayed? First place to start when you have a problem!

Thanks for the suggestion. I just checked and I'm getting a code 36, which I've been getting for a few months now. This is the MAF burn-off code, Over the past few months I've replaced the burn-off relay, power relay, MAF and ECM, I'm guessing I have a bad wire somewhere, but I've had this code for the past several months when I haven't had the IAC problem so I think it's probably not related, although it could be if I have a bad wire/ connection somewhere.

 

[tonybabb]

I'll do that

Have cleaned the IAC and Throttle body. The IAC may be sticking, or the passages carboned up. If they are clean you may need a new IAC.

Mike

Thanks, i'll try cleaning it first and see if that does the trick, although my baby has done 230K+ miles 99% with me driving it so it may need a new one by now, guess it doesn't owe me anything.

Thanks again.

Tony

 

[FForward]

After replacing the relays, maf, and ecm, did you erase the code 36. If you disconnect the battery for a few minutes it erases all codes. If you did that and the code 36 came back, check your wiring. I have heard it on here where the connectors are at fault quite often.

What have you done to the IAC anything? Have you taken it out and cleaned it?

 

[tonybabb]

Did that too

After replacing the relays, maf, and ecm, did you erase the code 36. If you disconnect the battery for a few minutes it erases all codes. If you did that and the code 36 came back, check your wiring. I have heard it on here where the connectors are at fault quite often.

What have you done to the IAC anything? Have you taken it out and cleaned it?

Yes, I reset the codes by disconnecting the battery, (I have done it so often I'm thinking about getting one of those battery quick disconnect switches !!). The odd thing is that after resetting the codes it works fine for maybe 5 or six engine start/ stop cycles, then the check engine light comes on, I have also looked and can see the MAF filament glowing when I shut down, so I know it's working.

Re the IAC, I haven't cleaned it, that'll be my next step. Looks like there's a gasket there, should it be replaced? I'll be heading to Autozone for the MAF cleaner tomorrow so might as well pick up a gasket - if they have them. Thanks for the suggestions.

 

[Hib Halverson]

Idle stability or no idle when hot problems can be caused by a faulty IAC. But they also can be caused by a faulty throttle body, faulty MAF, incorrect or faulty PCV valve along with a few other problems.

The first thing to do is to solve the problems that's setting the code 36 then move onto inspecting the IAC and the TB.

At 230,000 miles, if the engine needed a new throttle body, I would not be surprised.

 

[John Robinson]

One thing the Maf and Iac along with the tps and a couple of other sensors have in common is they all go into a common ground bundle in the wiring harness. The code is important in that it is telling you something is wrong with the signal to the ecm. The ecm will try to correct the bad signals and will eventually not be abel to get all the sensors information right so it ends up throwing a code for the last thing it can't compensate for. So at this point every wire and connector needs to be checked not only for clean contacts but for broken wires or bad grounds.

This is from my fsm for a 93 Corvette but it is relavent to any car with a tps.

Bymonitoring the output voltage from the TP sensor, the ECM can determine fueldelivery based on throttle valve angle (driver demand). A broken or loose TPsensor can cause intermittent burst of fuel from the injectors and cause anunstable idle, because the ECM detects the throttle is moving.

A word of caution do not back probe the wires for continuity unless you have removed all the connectors from the ecm. The voltage from the meter or continuity tester is bad for the ecm (like it can fry it) I prefer to use an old style meter with the needle to check for continuity. With the help of some small pins and jumper wires you can go from the ecm connector to the the corresponding pin on the sensor(assumeing you have a fsm that identifys what each pin on the ecm connector is for) . Now if you are showing continuity with the meter needle pegged and you shake the wire or move it you will be able to see if the needle on the meter moves. If it loses continuity you have isolated that wire as being bad.

Just curouis about how many miles are on the car. Hib makes reference to it's having 230,000 and I can not fingure out how he found the number. Because it is important to know the milage on a car in trouble. The higher or lower the milalge brings up different things that can be happening with a particular vehicle.