Adjusted TPS to 0.54, now idles at 1300
06-16-2018, 01:39 PM
#101
Just a standard regular filter. So apparently Advance no longer stocks Bosch MAFs for this car. So I have a store credit and need to choose between a Spectra, Cardone, and Carquest. Spectra/Carquest are new units and Cardone is remanu. It kinda seems like the forum feedback on these varies case by case. I could always keep the store credit and source elsewhere. Any feedback on brands?
I can't think of any other reason other than the MAF being bad that would cause it to idle high like that. I know pulling the MAF kicks it into a standard fueling map that guesstimates engine needs. But I'm curious if the issue is going to be a closed loop issue where one of the inputs could be bad. But the only two that come to mind would be 02 and MAF (with 02, MAF, IAT, CTS being the main players). I'm assuming the MAF is showing more air flow than what is actually flowing so the ECM is adding more fuel to compensate and leading to higher RPM. Journey, what a journey
I can't think of any other reason other than the MAF being bad that would cause it to idle high like that. I know pulling the MAF kicks it into a standard fueling map that guesstimates engine needs. But I'm curious if the issue is going to be a closed loop issue where one of the inputs could be bad. But the only two that come to mind would be 02 and MAF (with 02, MAF, IAT, CTS being the main players). I'm assuming the MAF is showing more air flow than what is actually flowing so the ECM is adding more fuel to compensate and leading to higher RPM. Journey, what a journey
06-16-2018, 07:39 PM
#103
Racer
Thread Starter
I think so long as any of those brands have a warranty to cover a lemon, you should be good. I agree with your deduction on the MAF. Crazy that this is most likely bad, as well as the TPS. The worst issues to hunt are two separate issues that manifest in similar ways.
I had some QD and hit it with the QD and it had no change. Figured why not try. I think this unit just crapped out. The Spectra touts it has a super durable circuit board, so i'll roll the dice...
06-17-2018, 02:20 AM
#104
Unfortunately, I have to wait until Monday for a replacement. I'm going to go with the Spectra. They seem to have the best reviews. I did fiddle with the car some. Removed the MAF and just let the car idle in the driveway and it rock solid holds a healthy 800 idle. Runs rich, but it idles like a champ
I had some QD and hit it with the QD and it had no change. Figured why not try. I think this unit just crapped out. The Spectra touts it has a super durable circuit board, so i'll roll the dice...
I had some QD and hit it with the QD and it had no change. Figured why not try. I think this unit just crapped out. The Spectra touts it has a super durable circuit board, so i'll roll the dice...
06-19-2018, 08:03 PM
#105
Racer
Thread Starter
I'm defeated. New Spectra MAF and same result. I traced all of the MAF wiring and it has passed the visual test. While running, unplugged o2, CTS, IAT, all with no change to the 1500 idle. Even unplugging MAF at this point only dropped it to 1000. Went through IAC reset process again, no change.
At this point, the only thing I can think of is that I have a bad ECM/PROM that is causing the issue. I did read some time back that when ECMs go bad, they tend to be temperature sensitive. The only real variable in the car between last month and now is that the temps are now in the 90s here in NC. I might try the old refrigerator trick where you let the ECM chill out in the fridge for like an hour and then pop it in the car and see if it behaves different. I'll post a new thread and see if we can get some more heads in on this. I can't thank you all enough for all of your time up to this point. I still welcome thoughts my friends
At this point, the only thing I can think of is that I have a bad ECM/PROM that is causing the issue. I did read some time back that when ECMs go bad, they tend to be temperature sensitive. The only real variable in the car between last month and now is that the temps are now in the 90s here in NC. I might try the old refrigerator trick where you let the ECM chill out in the fridge for like an hour and then pop it in the car and see if it behaves different. I'll post a new thread and see if we can get some more heads in on this. I can't thank you all enough for all of your time up to this point. I still welcome thoughts my friends
06-19-2018, 08:21 PM
#106
So you say on your idle adjust procedure you get the car at 450rpms (barely running) as called for, and when you plug the iac back in and restart it shoots up to 1500 rpms. I don't see how but I am interested. There has to be a code.
Last edited by xrav22; 06-19-2018 at 08:23 PM.
06-19-2018, 08:22 PM
#107
I'm defeated. New Spectra MAF and same result. I traced all of the MAF wiring and it has passed the visual test. While running, unplugged o2, CTS, IAT, all with no change to the 1500 idle. Even unplugging MAF at this point only dropped it to 1000. Went through IAC reset process again, no change.
At this point, the only thing I can think of is that I have a bad ECM/PROM that is causing the issue. I did read some time back that when ECMs go bad, they tend to be temperature sensitive. The only real variable in the car between last month and now is that the temps are now in the 90s here in NC. I might try the old refrigerator trick where you let the ECM chill out in the fridge for like an hour and then pop it in the car and see if it behaves different. I'll post a new thread and see if we can get some more heads in on this. I can't thank you all enough for all of your time up to this point. I still welcome thoughts my friends
At this point, the only thing I can think of is that I have a bad ECM/PROM that is causing the issue. I did read some time back that when ECMs go bad, they tend to be temperature sensitive. The only real variable in the car between last month and now is that the temps are now in the 90s here in NC. I might try the old refrigerator trick where you let the ECM chill out in the fridge for like an hour and then pop it in the car and see if it behaves different. I'll post a new thread and see if we can get some more heads in on this. I can't thank you all enough for all of your time up to this point. I still welcome thoughts my friends
06-19-2018, 08:31 PM
#108
Racer
Thread Starter
06-19-2018, 08:33 PM
#109
Yessir. I get it settled right where the tac will bounce between 4-5. Key off, reconnect IAC, restart, car will idle nice until I give it the first rev and then when coming off rev, it'll settle on 1500.
Thanks man, we'll get this thing figured out soon enough. I just hope this doesn't turn me bitter on the C4s. If this were an LS with modern controllers, etc., i'd be all over it. I was committed to learning the older tech for "fun projects" but this has sorta crossed over the fun line
Thanks man, we'll get this thing figured out soon enough. I just hope this doesn't turn me bitter on the C4s. If this were an LS with modern controllers, etc., i'd be all over it. I was committed to learning the older tech for "fun projects" but this has sorta crossed over the fun line
06-19-2018, 10:11 PM
#110
Team Owner
Yessir. I get it settled right where the tac will bounce between 4-5. Key off, reconnect IAC, restart, car will idle nice until I give it the first rev and then when coming off rev, it'll settle on 1500.
Thanks man, we'll get this thing figured out soon enough. I just hope this doesn't turn me bitter on the C4s. If this were an LS with modern controllers, etc., i'd be all over it. I was committed to learning the older tech for "fun projects" but this has sorta crossed over the fun line
Thanks man, we'll get this thing figured out soon enough. I just hope this doesn't turn me bitter on the C4s. If this were an LS with modern controllers, etc., i'd be all over it. I was committed to learning the older tech for "fun projects" but this has sorta crossed over the fun line
06-19-2018, 10:47 PM
#111
Racer
Thread Starter
Believe me, I 100% agree with you. Here’s the dilemma. Do I spend $100 on an X-ray 2500 or $60(after discount pricing) on a remanu ECM. If I do get the scanner and find out the steps are at like 150, then I’m just going to make the same decision, just have more info. At this point it’s a new MAF and IAC and I’ve gone through the reset process more times than I care to admit. If it’s a vacuum leak, then it’s the best kept vacuum leak in the history of vacuum leaks.
The common denominator here seems to be an inability of the ECM to maintain an idle less than 1500 unless the MAF is disconnected. We eliminated MAF. So we’re down to what happened when the MAF was disconnected. ECM went into default fuel tables. Idle drops right to 800. Runs rich, but runs. This has got to be an engine management issue, not an IAC or TB set screw issue. There just seems to be a basic inability of the ECM to command a proper idle
The common denominator here seems to be an inability of the ECM to maintain an idle less than 1500 unless the MAF is disconnected. We eliminated MAF. So we’re down to what happened when the MAF was disconnected. ECM went into default fuel tables. Idle drops right to 800. Runs rich, but runs. This has got to be an engine management issue, not an IAC or TB set screw issue. There just seems to be a basic inability of the ECM to command a proper idle
06-20-2018, 07:42 AM
#112
Team Owner
Believe me, I 100% agree with you. Here’s the dilemma. Do I spend $100 on an X-ray 2500 or $60(after discount pricing) on a remanu ECM. If I do get the scanner and find out the steps are at like 150, then I’m just going to make the same decision, just have more info. At this point it’s a new MAF and IAC and I’ve gone through the reset process more times than I care to admit. If it’s a vacuum leak, then it’s the best kept vacuum leak in the history of vacuum leaks.
The common denominator here seems to be an inability of the ECM to maintain an idle less than 1500 unless the MAF is disconnected. We eliminated MAF. So we’re down to what happened when the MAF was disconnected. ECM went into default fuel tables. Idle drops right to 800. Runs rich, but runs. This has got to be an engine management issue, not an IAC or TB set screw issue. There just seems to be a basic inability of the ECM to command a proper idle
06-20-2018, 07:50 AM
#113
Racer
Thread Starter
I've been doing some more digging and reading through years of high idle threads. There seems to be this common theme of possibly having a stuck EGR valve. Essentially creating an internal vacuum leak. Thoughts? I'll do the fridge test tonight and see if that helps the ECM or not.
06-20-2018, 09:25 AM
#114
As with all C4s, it all comes down to what order you want to spend your money; savings is not an option lol.
I've been doing some more digging and reading through years of high idle threads. There seems to be this common theme of possibly having a stuck EGR valve. Essentially creating an internal vacuum leak. Thoughts? I'll do the fridge test tonight and see if that helps the ECM or not.
I've been doing some more digging and reading through years of high idle threads. There seems to be this common theme of possibly having a stuck EGR valve. Essentially creating an internal vacuum leak. Thoughts? I'll do the fridge test tonight and see if that helps the ECM or not.
06-20-2018, 07:39 PM
#115
Racer
Thread Starter
Agreed. I ordered an ALDL to USB today along with the drivers and ADX file needed to scan the car. The ECM freezer trick did nothing. I'm still betting on a bad ECM or PROM though. I can't imagine a sensor or input would cause this much trouble. I'm out of town tomorrow though the weekend, so Monday i'll post back with some data...
06-20-2018, 08:11 PM
#116
Agreed. I ordered an ALDL to USB today along with the drivers and ADX file needed to scan the car. The ECM freezer trick did nothing. I'm still betting on a bad ECM or PROM though. I can't imagine a sensor or input would cause this much trouble. I'm out of town tomorrow though the weekend, so Monday i'll post back with some data...
06-25-2018, 09:50 PM
#117
Racer
Thread Starter
. I feel like Odysseus coming back home after this journey
06-25-2018, 10:09 PM
#118
Man, it's fixed! You are not going to believe how stupid the fix was. I'm ashamed. I got the cable in and got TunerPro RT going. I only got like 5 outputs, but it was all I needed. Long story short, I think my multimeter was the culprit. I left the TB with the set screw almost backed all the way out, enough that it wasn't advancing the blades and the ECM was showing TPS volts at 1.3. I adjusted the set screw in about 5 turns from point of contact and then adjusted the TPS per the ECM read out to 0.54. Holy hell, it idles right at 750.... I need to go through the min idle reset process again using the ECM data. I took the car out and it felt great (for a 29 year old sports car lol). I just ran out of daylight to keep working. Lesson learned, use scan data . I feel like Odysseus coming back home after this journey
. I feel like Odysseus coming back home after this journey
06-25-2018, 10:23 PM
#119
Racer
Thread Starter
06-25-2018, 10:28 PM
#120
It's crazy though, I actually used the multimeter on other things outside of the car and it worked just fine. I think for some reason I was picking up some resistance on that middle ECM TPS pin. It showed 5v on the others just fine. Now I can get back to finishing up the cosmetics on the resto and start thinking about those power upgrades! Thanks again man, you'll have to PM me some contact info and i'll send over some alcohol of your choice