2.8 idle issue with iac plugged in (Page 1/1)
pontiacfierokid1985 AUG 15, 07:43 PM
Ok got a bit of confusion going on here that doesnt make sense when i have the iac plugged aldl not by passed the idle is all over the place 1100-1800 rpm. I sprayed for vac leaks none found held finger over hole in tb bore and motor stalls out immediately. Now if i go and plug the aldl port to bypass it im getting a steady idle of 1000 rpm the whole time running. Thinking i fugure its got to be a bad iac i replaced it and still getting the same issue. What the heck can be going wrong with this dang thing i want to register the car on monday but want all the faults to be corrected while it has no plates attached
pontiacfierokid1985 AUG 15, 08:25 PM
So was playing around with the egr valve and noticed a slight hiss coming from it. I moved the diaphragm up and the idle kinda smoothed out it bogged but stayed on 1100 rpm looks like im deleting it cause since that is 50 bucks from parts store also guessing tube is cracked as well so ill just get the gasket set that comes with all the intake gaskets and egr gaskets and blocked them off. Rock auto for everything is like 20 bucks but im not waiting a week for the parts to come in want this damn car done and running correctly. My last fiero was like that and steady idle was 1000 rpm and drove with no problem check engine light never came on either. Would this be ok to do you think?

[This message has been edited by pontiacfierokid1985 (edited 08-15-2019).]

Spoon AUG 16, 03:36 PM
Open loop vs closed loop,,,Seems like one of your sensors is out of wack in closed loop. In open loop the sensors are not controlling anything and a fixed program is running the show. A slow acting O2 sensor will lean out and richen the fuel mixture slow enough to allow the rpm to rise above & below spec.
If you haven't already, swap it out for a known good one or buy a new one . I'd start there.

Spoon

------------------
"Kilgore Trout once wrote a short story which was a dialogue between two pieces of yeast. They were discussing the possible purposes of life as they ate sugar and suffocated in their own excrement. Because of their limited intelligence, they never came close to guessing that they were making champagne." - Kurt Vonnegut

pontiacfierokid1985 AUG 16, 07:46 PM
Thing is im not getting any codes for bad o2 sensor. It just doesnt make sense i just dont wanr to keep throwing parts at it like im doing i know this is a simple fix. My question is when its in bypass mode why does it idle steady at 1000 rpm’s but as soon as it comes out of that it acts up.
pontiacfierokid1985 AUG 16, 11:54 PM
Ok new update flashed the ecm to see if any trouble codes are stored and i have code 21 low tps voltage and code 22 so seems like the throttle position sensor is faulty which im picking up tomorrow hopefully this fixes the problem with the idle situation
pontiacfierokid1985 AUG 17, 12:06 AM
Ok new update flashed the ecm to see if any trouble codes are stored and i have code 21 low tps voltage and code 22 so seems like the throttle position sensor is faulty which im picking up tomorrow hopefully this fixes the problem with the idle situation
Spoon AUG 17, 06:46 PM
"A word to the wise",, The codes the ECM reports tells you what is being affected by the problem.

Example, a mouse chews on a wire down to the last strand so the 5 volts in that wire is now 1 volt to the TPS. Error code 22.
You can rush out and buy a dozen TPS sensors and none will correct the error because the TPS component is being effected by the bad wire in this example.

OBD-1 codes only give you a clue as to where to start looking, not replacing, as a lot of mechanics sometimes do. Get yourself a multimeter and check voltages, grounds and resistance before running off and buying components only to find they did not solve your problem.

If you choose to buy the component first, then you should ask yourself, "Do I feel lucky".

In addition OBD-1 is not sophisticated enough to report a slow acting O2 sensor. All it knows is it's still switching rich to lean repeatedly.

This may help.
https://www.youtube.com/watch?v=ljC8yCP5v1k


Spoon


------------------
"Kilgore Trout once wrote a short story which was a dialogue between two pieces of yeast. They were discussing the possible purposes of life as they ate sugar and suffocated in their own excrement. Because of their limited intelligence, they never came close to guessing that they were making champagne." - Kurt Vonnegut

[This message has been edited by Spoon (edited 08-17-2019).]

claude dalpe AUG 17, 10:44 PM
Perfectly agree with spoon
pontiacfierokid1985 AUG 18, 02:25 PM
Well i checked wiring first and im getting the 5 volt reference from the ecm on the top pin of the tps connector. When i do the tps sweep on the middle pin im getting .49 volts and i push the lever all the way to the bottom on the tps it goes to 4.98 so close to 5 volts. That tells me that the wiring from the ecm to the sensor is good and no shorts are present or open circuits.
Spoon AUG 22, 10:16 PM
Pull your center console to gain access to the ECM. Recheck your TPS circuit. With probes on terminals have an assistant wiggle, poke & prod the harness wires at the ECM and at the TPS connector and observe of any loss of signal on your meter.
Also move the TPS arm very slowly thru its travel range while looking for a steady movement on your meter. Any needle jerks indicate a compromised TPS.

I once had a situation with my 2.8 that would shut the engine off while traveling down this highway. I'd push the clutch in and start it back up. It turned out to be a poor connection at the ECM. A white wire leading back to the ignition control module. I could press against that wire ever so slightly and the engine would abruptly shut off.

Here's a schematic from the archives that may help you.

Spoon

------------------
"Kilgore Trout once wrote a short story which was a dialogue between two pieces of yeast. They were discussing the possible purposes of life as they ate sugar and suffocated in their own excrement. Because of their limited intelligence, they never came close to guessing that they were making champagne." - Kurt Vonnegut