Diagnose IAC and Idle Speed - Chevy Camaro 305 TBI

[@chrisgoped69]

Morgan’s dad is a developer but a very big kind hearted guy caring about his daughter and family

[@mindinew]

Glad to hear your wellbeing which is the most important thing.

[@bitsofwisdom460]

Yes, I'm doing very well now, thank you.

[@6904gabriele]

Hi Dan!
Finally I’ve solved my IAC trouble!
One of the 4 plug wires was broken,no SES light,no codes on WinAldl too.I have used my IAC tester in combination with a scope,I have made a double IAC plug and tested engine running with two IAC,after receiving and rewiring the new plug,now my engine runs quite again…in Drive too 😊!Strange to see the IAC pintle moving back and forward when idling,with only 3 wires and also strange that reaction when put in Drive or reverse.That strange problem causes my Camaro sitting in the garage for 2 years!

[@bitsofwisdom460]

Good to hear that you found the issue. If I remember correctly, the IAC has two coils. I expected that they operate in tandem, but perhaps there is a built in override that if one coil (or feed circuit) is bad, the idle is elevated.

[@6904gabriele]

Very informative video Dan,you are a nice person.Let‘s investigate more deep now with your explanations and your charts. I have the IAC tester tool,it‘s a Thexton 398 and runs well!

[@bitsofwisdom460]

Glad to hear that you have the tool. That should make the testing easier.

[@luckystrike936]

really happy you made this channel i cant find anyone local who knows much about these systems i bought an 89 camaro 5 years ago and 3 out of the 5 its been stalling at idle and just now think i found the problem it seems the used ecm i put in it cured it for now problem is now i cant use my scan tool on it

[@bitsofwisdom460]

It is hard to say, the ECM and PROM run the diagnostic interface. Did you keep the cal PROM from the old ECM? I had a problem with a different GM car that had an aftermarket PROM that broke the scan tool interface. It still flashes codes, but won't send data.

[@luckystrike936]

@@bitsofwisdom460 i transferred the oem chips to the ecm that works and the check engine light flickers so my hope is the chip just didnt seat properly funny you mentioned those aftermarket chips ive got one and they tell you in the instructions you have to put the oem chip back in if you take to a mechanic

[@brockkellenberger]

Thank u for this content. U do a great job explaining things. I appreciate ur videos.

[@bitsofwisdom460]

I appreciate that!

[@mikebruegger8654]

Nice information and effort as usual! I had some idle issues and had found my IAC valve to have come apart in place! I simply put it back together, reset it and problem solved! All of us watching you have a great reference in the form of a live knowledgeable person! Thank you so much for your time. I'm still fighting Nox issues with smog check but all the systems are working. My EGR opens as commanded but it is shakey while open and not simply open without some movement. I don't know if this is normal or if maybe the exhaust back pressure is too low to help. I did replace muffler with a GMMG chambered cat back system. Something else I noticed on the smog test is that at 15 and 25mph runs on the dyno, the engine is running in the 1300 rpm range and I do not believe the EGR duty is called unless over 1500rpm. When test driving with scan hooked up, that seems to be the case. If the EGR is not opening even at the testing speeds, it may show high Nox. Maybe they could do the test in 1st or 2nd gear to increase rpm? I am going to road test it that way and see if that may work. I did confirm that the EGR is opening when the scan says so as I had a camera under the plenum watching in real time. Glad you are feeling better! 😊 😊

[@bitsofwisdom460]

The EGR on these engines is a little bit of a challenge to diagnose or predict because of the negative backpressure EGR valve. The challenge is that negative exhaust pressure will release the vacuum signal and tend to close the valve, even if a duty cycle is commanded. The engine exhaust has pulses both positive and negative, with more negative pulses at light load. Not sure if your car's calibration is different, but in my car and in the data I have previously posted, I get EGR command starting at about 1150 to 1200 RPM with light throttle. I am right now looking a data set of 50% EGR at 1125 RPM at 6% TPS. Then the book says that at idle, the valve will release the vacuum because of the negative pulses. I think you will see negative pressure diminish with increasing throttle and speed. So, how much EGR will I actually have at the above condition?
Your thought about the chambered exhaust could be a factor, but frankly I would be surprised if it was the cause. I don't know, of course, but I would expect that the catalyst would provide enough back pressure to maintain the pulsations in the manifolds and the muffler being much further downstream would not have a great effect. Could the EGR valve have an internal issue?

[@mikebruegger8654]

@@bitsofwisdom460 my EGR is new and the tests in the factory service manual all pass. The scan tool only shows 0 or 100% and never anything else. I read that drilling the hole very slightly bigger on the EGR at the vaccumm line attach point will allow it to open easier. My car is in excellent shape and runs very well. Very bewildering for sure.

[@bitsofwisdom460]

@@mikebruegger8654 Mike, I'm scratching my head. I know that California calibrations were usually different than 49 state, but it doesn't make sense to me that your car would have less EGR than mine. Given Calif emissions, I would expect perhaps more EGR. Also, the whole point of the PWM driven EGR solenoid is to provide variable flow, not just 0 or 100%, that seems odd. The book indicates pulse width is set by air flow, coolant temp and engine speed. It would be a calculation probably based off of a look up table with speed and throttle or similar. Again, my car will provide 30 to 50% duty cycle command at just off idle with light positive throttle. It would make me wonder if there is a problem with either the PROM or ECM. I know there are trouble codes for the PROM, but I don't know how thorough they are. It would be tempting to find someone who can read out the PROM and see if the EGR tables look correct. Alternatively, could the ECM have a problem with the EGR PWM circuit so that it is only running zero or 100% regardless of command. I don't know where the duty cycle data for the scan tool originates. Is it the command to the PWM circuit or is it the actual output of the PWM driver circuit? Just food for thought at this point. I'm seldom in favor of blindly replacing parts.

[@mikebruegger8654]

@@bitsofwisdom460 I will see if I can find someone to check ECM and check for possible errors. I appreciate your knowledge and time about this. Even the gentleman at the smog station is lost as to why. I can say that the EGR moves open in a shivering way and I'm not sure if it should open cleanly or if it is sorta opening at variants of full open as the scan tool says. Have a great day.

[@Dbomb81]

I have a '91 305 TBI 5 speed Manual with the same issue but only at idle. Tried replaced the TPS. Tried a new Throttle body gasket kit. Still the same thing.

[@bitsofwisdom460]

Well, I can only suggest to walk through the trouble trees. As you can see, there are a number of possible causes for idle speed to be abnormal.

[@6904gabriele]

Hai Dan,my researces on my IAC continues.
I've (visually too) noticed something: my ecm retract the IAC when I shut off the engine and not in the start procedure.
Also on WinAldl shutting off the engine the IAC counts jumps to 160.
Now a question for you:on the Flag Data what is the”Reference Pulse Occured” flag related to?
I noticed that flag pulsing every 2 seconds in alternance with the”Rich Flag”Flag.

[@bitsofwisdom460]

I am not certain, but I think the reference pulse is the distributor pickup coil producing spark trigger pulses.
When you key off, the data stream stops and WINALDL will go to some default value that won't be accurate. The value for key on before cranking would be valid. The IAC could still retract, but I don't know if it is a good reading. Exact opening on a start is hard to predict. It ought to be near wide open, but the calibration engineers need to program it to close down quickly when the engine fires so that it doesn't flare too high.

[@FSEVENMAN]

Great video Thank you😊

[@MrEricMcCullough]

Please help! I’ve tried changing just about everything I know to and my car still has rough idle. I purchased an ALDL cable hoping to see more and it led me to change more parts but still no luck. It keeps flagging that the AC and AC clutch are engaged but it’s not. Any ideas?

[@bitsofwisdom460]

Long distance diagnostics is a challenge, but I'll try to help. Tell me a little more about exactly your engine combination, symptoms and ALDL data. Do you get closed loop? All the vacuum lines good, including line to the purge canister? Fuel pressure ok? Just a starting point.

[@MrEricMcCullough]

@@bitsofwisdom460 I have an 88 Iroc 5.0L 305. 1100 rpm idle, exhaust smell, not smooth rev’s, lacks power. I don’t believe I’m getting the closed loop. I’ve tried replacing the IAC and calibrating with no luck. Along with O2 sensor, plugs, wires, distributor cap, coil, ignition rotor, ignition control module, alternator, verified ohms and node light test on injectors, EGR, fuel regulator, MAF temp probe. I’ve checked vacuum hoses for leaks but I have not pulled a vacuum on the system. I did the fuel pressure test and it passed. I Havnt done a compression test. Recently believed I had found the culprit by finding some trapped pressure between the shredder valve and the fan pressure switch. At the time the AC flag stopped and the car idled down and the rev’s were smooth. Then it’s like it learned what was going on and went back to the rough idle. It also did this a while back when I borrowed a buddies MAF sensor. It ran great and we thought we found it, but then it learned what was going on and recalculated to compensate for it. Most things in win ALDL look ok to me along with no check engine codes. Just the flag data saying AC enabled on/off every 3 seconds. My thinking is the computer is telling the car to idle up and down based off this and equaling the rough idle.

[@MrEricMcCullough]

@@bitsofwisdom460 I have a 88 5.0l 305 TPI. It’s had a rough idle for almost 6 months now and I still Havnt been able to find what’s causing it. There’s a hesitation when you rev it up along with 1100 RPM idle. It feels like it’s shuddering some along with exhaust smell. I don’t believe I’m ever going into closed loop. No error codes. I can’t find any vacuum leaks. I’ve changed the FPR and fuel pressure test seems good. I’ve changed about every common part that forums say could be the issue with no luck. What keeps flagging in WinALDL is the “A/C enabled”. Thought I had it the other day when I found some pressure trapped on the fan pressure switch. Switch checked out good and it stopped flagging. At that time it ran perfect. Since then it’s back to doing it again.

[@bitsofwisdom460]

@@MrEricMcCullough Well, a couple of thoughts. The A/C switch might cause a small idle speed increase and would turn on the fans, but shouldn't hurt idle quality. You can try unplugging the switch to see if it is intermittent.
WINALDL ought to give you a closed or open loop signal and a rich / lean signal. It would help to know where you are running. I would suggest comparing your data to my running engine. Look at the parameters and see if the sensor readings make sense. Especially is mass air flow proper? You might even try unplugging the MAF just for a check to see what happens.
My road test run of WINALDL data is in this video:
th-cam.com/video/cmxqhTReRUk/w-d-xo.html
My cold start data from my Actron tool is here:
cold start data2.movie.mp4
The Actron tool does have a couple of oddities in conversion that WINALDL fixes.
Remember that running a scan tool or WINALDL with the 10k resistor will elevate the idle to 1100 and advance timing on most engines.

[@MrEricMcCullough]

Thank you for your reply and apologies for late reply. I’ve been trying to chase down another issue that came up before I can get back on this one. Evidently the alternator went out and burned some things up. My high beams wouldn’t work and finally tracked it down to being the dimmer switch. Now the new alternator has voltage on the red wire that comes from the starter, but it doesn’t have voltage on the brown or the light brown/white stripe wire. From what I’ve red one of these should have voltage when you turn the ignition on and also give voltage to the cooling fan relay coils. My fans are running but not how they are supposed to. They work in tandem instead of independently. Once I get this sorted out I’ll be able to give you more data compared to your video.

[@apethings7671]

AIC has kicked my but 3 time on 93 p/u cracked housing was latest fiasco

[@geremychubbuck3730]

Glad to hear that your kidney stone is gone. 👍They are the worst

[@bitsofwisdom460]

Thank you! Yes, they are really tough. I was blessed that this one moved through fairly fast. I have had them persist over weeks before.

[@ScottsFormula350TPI]

Can you give me advice on where to go next? I admit though I have not started it yet today and battery has been unhooked over an hour. Oh,Good morning by the way and glad to hear of your improvinig health.

[@bitsofwisdom460]

Which coolant sensor code do you have? If you have a new sensor, you start looking at wiring and connections. High temp or low temp? High looks for a short or short to ground and low looks for an open. Scan tool helps or DVM reading the circuit at the ECM connections. Sensor has low resistance hot and high resistance cold.

[@ScottsFormula350TPI]

@@bitsofwisdom460 my code was 42 and 45. 42 has been traced we believe its not the ignition modulator itself but the 2 prong female connector, when i unplugged it the thing literally disentigrated in my hand. I installed icm anywhoos.hooked up wires without plastic clip as it blew up, car started but after 90 seconds 2 min car went into a limp mode or whatever and light came back on. Weve done exaughstive testing on almozt every sensor and all have proper grpund and ecm return voltage. Left with plug and icm wires. Connectors are all rustyand everything.

[@bitsofwisdom460]

Ok, I was looking at your video that indicated a coolant sensor issue. If you have a wiring concern, then yes, a fresh ICM connector with clean pins that fit properly is important. A 42 would mean that you're running at base timing because EST isn't working properly or the "set timing" lead is not connected.

[@ScottsFormula350TPI]

@@bitsofwisdom460 im stupid est?

[@bitsofwisdom460]

@@ScottsFormula350TPI EST= Electronic Spark Timing. ECM reads speed / position data from ICM. Adds in data from other sensors to calculate timing needed and sends EST timing signal back to the ICM to trigger spark. Bypass lead disconnects to set base timing.