Idle issue with 94 Lumina 3.1 V6

[Reckless Driver]

I have a 94 Lumina with the 3.1 V6 engine. It idles high and then low constantly at idle and will stall. Going down the open road it runs fine but at low speeds, it jerks and does not want to go.
I got 3 error codes off the computer. 35, 44 and 45. 35 is the idle speed sensor. I replaced that, and I also replaced the front oxygen sensor. I have checked and double checked for vac. hose leaks and have none.
After I clear the error codes, they come right back, and I still have the same problem. I think this may be the EGR valve, but I am not certain?
Does anyone have any ideas? I have been told it could be both the Mass Air Flow Sensor and Idle Positioning Sensor.
Shouldn't I be getting these error codes coming up on the computer, if this were true? Any of these items are over 100 dollars each with the EGR being 190 bucks.
I NEED to know for certain, before spending that kind of Money. I have no problem with going to the salvage yard for these items too, but it would help to have a pretty good idea, rather than but all of these items and have only 1 causing my problem.

ANY solid ideas would be greatly appreciated!!

Thanks,

Randy

[DnaProRacing]

Save a few bucks, try this first; buy a can of seafoam transtune, a can of regular seafoam, and a can of seafoam deepcreep.
drain a pint of tranny fluid out of your transmission and replace it with the pint of transtune. this will lubricate the tcc.
next, pull the hose off your pcv valve while the car is running and pour some of the regular seafoam into it. pour in slowly "enough to coat the entire inside of the line". if the car stalls, leave it off for 15 minutes "or turn it off", then put the pcv line back on and start er up. it should toss a buttload of smoke out the exhaust.
lastly, remove your intake pipe, spray deepcreep into the manifold, coat it all very good, use a toothbrush to clean out any visible carbon build up. now remove your egr valve and spray deepcreep in the hose and toward the manifold. clean all of this out as good as you can get. put it all back together, dump the remainder of the regular seafoam into your gas tank. let us know if this cures your current issue...

[Blue Bowtie]

Reckless,

The "35" is for the Idle Speed Control (ISC), not an "Idle Speed Sensor" since there is no such device. The device is used to admit extra air to maintain engine RPM. It does not "sense" the idle RPM, and offers NO direct feedback to the ECM. The system relies upon what the ICM detects as RPM change as a result of the ISC inputs. The ECM can detect if the ISC stepper motor coils are either open or shorted, however, and generating such an error code could be the result of a poor connection between the ISC and ECM. That would also explain the poor idle speed regulation. Since you mentioned that you have replaced the ISC (unfortunate, since it probably wasn't the problem), I'd suspect a connection issue.

Furthermore, there is no such thing as an "Idle Positioning Sensor". There is a Throttle Position Sensor (TPS) but it is also closely monitored by the ECM and if the signal is out of range or intermittent, a code for that would be generated quickly. As a double-check, you can measure the voltage output of the TPS to verify its operation.

Teh "44" and "45" are indicating both a lean and rich condition during normal cruise. That can be due to a problem in the O² circuit, or a significant vacuum leak or fuel delivery problem.

If you suspect the EGR, it can be removed, cleaned, and inspected.

[Reckless Driver]

Hey, thank you for the multitude of useful information, I do really appreciate that. But not the smug attitude. If I was a licensed mechanic and knew every single term for everything, there would be no need for me to come on here to ask for help.

I will try the suggestions in the first post to my questions and see what happens. Thanks

Originally Posted by Blue Bowtie

Reckless,

The "35" is for the Idle Speed Control (ISC), not an "Idle Speed Sensor" since there is no such device. The device is used to admit extra air to maintain engine RPM. It does not "sense" the idle RPM, and offers NO direct feedback to the ECM. The system relies upon what the ICM detects as RPM change as a result of the ISC inputs. The ECM can detect if the ISC stepper motor coils are either open or shorted, however, and generating such an error code could be the result of a poor connection between the ISC and ECM. That would also explain the poor idle speed regulation. Since you mentioned that you have replaced the ISC (unfortunate, since it probably wasn't the problem), I'd suspect a connection issue.

Furthermore, there is no such thing as an "Idle Positioning Sensor". There is a Throttle Position Sensor (TPS) but it is also closely monitored by the ECM and if the signal is out of range or intermittent, a code for that would be generated quickly. As a double-check, you can measure the voltage output of the TPS to verify its operation.

Teh "44" and "45" are indicating both a lean and rich condition during normal cruise. That can be due to a problem in the O² circuit, or a significant vacuum leak or fuel delivery problem.

If you suspect the EGR, it can be removed, cleaned, and inspected.

[Reckless Driver]

Hi ProRacing. Thank you for all of your ideas and useful information. And thank you for the respectfulness of your reply.

Must not have been too hard to understand my questions, even without the EXACT terms used by mechanics?

Seafoam is not too bad in price so I am going to go with this suggestion first. And we will just have to see what happens. I will let you know how it works out. Again, thank you!!

Originally Posted by DnaProRacing

Save a few bucks, try this first; buy a can of seafoam transtune, a can of regular seafoam, and a can of seafoam deepcreep.
drain a pint of tranny fluid out of your transmission and replace it with the pint of transtune. this will lubricate the tcc.
next, pull the hose off your pcv valve while the car is running and pour some of the regular seafoam into it. pour in slowly "enough to coat the entire inside of the line". if the car stalls, leave it off for 15 minutes "or turn it off", then put the pcv line back on and start er up. it should toss a buttload of smoke out the exhaust.
lastly, remove your intake hose, spray deepcreep into the manifold, coat it all very good, use a toothbrush to clean out any visible carbon build up. now remove your egr valve and spray deepcreep in the hose and toward the manifold. clean all of this out as good as you can get. put it all back together, dump the remainder of the regular seafoam into your gas tank. let us know if this cures your current issue...

[Blue Bowtie]

No attempt at being smug nor condescending here. We never know to what/whom we might be replying, and have no idea of their level of experience or expertise. I only wanted to be certain you understood the function of the device so we can proceed with the diagnosis and repair. Incidentally, on GM vehicles, it is also known as an "IAC" (Idle Air Control, because that's what it does).

If the "35" is repeating after having replaced the IAC, there is likely a problem with the connection between the IAC and ECM, or a problem with the output transistors in the ECM itself. The latter can be a lot harder to repair, and ECM replacement would likely be easier. Unfortunately, you might need to access the ECM and expose its connectors to be able to check the continuity between the ISC connector and ECM connector.

A somewhat easier way to determine if the IAC is getting pulses from the ECM is to remove it from the throttle body, place it securely in a plastic bag with the electrical connector attached (in a bag so you don't lose the pintle and spring), place a jumper in the ALDL connector A and B terminals, and turn on the ignition without starting the engine. If the IAC coils are getting pulses from the ECM, the pintle and spring should extend (and possibly all the way until it falls apart, which is why it's in a plastic bag). If it doesn't move, there may be an ECM or wiring problem.

This will only work on older, non-OBD-II engine controls, and I believe your '94 would be included. If the ALDL connector under the dash has terminals in the A and B positions, it should work:



There is also the possibility of a general poor connection issue with the ECM, which might also explain the rich and lean exhaust sensor codes.