high idle - update - Page 3 - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


1992-1999 Series I L27 (1992-1994 SE,SLE, SSE) & Series II L36 (1995-1999 SE, SSE, SLE) and common problems for the Series I and II L67 (all supercharged models 92-99) Including Olds 88's, Olds LSS's and Buick Lesabres Please use General Chat for non-mechanical issues, and Performance and Brainstorming for improvements.

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Old 12-30-2007, 01:07 PM   #21
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Quote:
Originally Posted by BMWhound
Whadda think? Am I on the right tracker here?
Yes, keep up the good work! If you have another MAP to try, do it. BTW, you have checked, cleaned and verified that the IAC is functiong properly?
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Old 12-30-2007, 02:57 PM   #22
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Z,

I put my MAP sensor from my truck in the car and read the output. it'* 1.5 vdc. So the sensor must be bad. Went to AZ, picked up a new MAP sensor, new ECT sensor. replaced both, unhooked the batt cable, hooked back up, cleard all codes - had 4 codes and started car. still idles @ 1000 rpm. Also the intake absolute manifold pressue still reads 4.6 - 4.7 in hg (from scanning software) Whats up with that? Shouldn't that be reading the 17.5 in hg now? PCM ? . I feel like I just wasted 55.00 bucks. What do I do now ???

Yes, I have verified that the iac is working and it is cleaned.

I also checked the output from the brand new MAP sensor. It was also 1.4 - 1.5 vdc and varied with the throttle.
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Old 12-30-2007, 05:28 PM   #23
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When you tested voltage on the original MAP sensor, you said that you had .115v, was that correct, or was it 1.5v? Now, when you installed the MAP sensor from your truck and got the 1.5v reading, was that @ idle? If so, that would indicate proper voltage for high vacuum. Don’t get discouraged, if your original MAP silicone seal was missing and the reading was actually .115v @ idle, you needed a new one anyway.

You have no other choice now except to get a good scan of all PCM inputs & outputs. You have to know how the PCM is interrupting sensor inputs. I have seen several PCM’* on 96’* fail to use correct sensor input, and the scanner should show that. You need someone well versed in what the correct readings should be and how to interrupt the information given. This is way beyond the typical AutoZone employee!

Example; recently I had a 96 Series II VIN-K with all perfect sensor voltage output, however, when looking at the reading on the scanner, it was different. In this particular case, code P0122 was present which indicated the TPS low circuit voltage (High idle @ 1500 rpm). Reference voltage measured @ the TPS was 5.0v & idle was .5v (Perfect) When I looked at the TPS scanner readings, the TPS voltage was 1.112. Like you, I had a spare (new) TPS in stock and put it in only to find I had the exact same scanner reading. Needless to say, the PCM was at fault and was skewing the voltage input. Finally, a new PCM resolved the issue!

Some scanners may show MAP voltage, while others use an interpolation of voltage to show in hg. If you have 17.5 in hg on the engine @ idle, of course, vacuum is fine.

BTW, sorry but I don't recall, have you checked & cleaned the EGR?
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Old 12-30-2007, 08:01 PM   #24
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When you tested voltage on the original MAP sensor, you said that you had .115v, was that correct, or was it 1.5v?
Positive - .115 volts I checked it several times.

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Now, when you installed the MAP sensor from your truck and got the 1.5v reading, was that @ idle?
yes sir.

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If so, that would indicate proper voltage for high vacuum. Don’t get discouraged, if your original MAP silicone seal was missing and the reading was actually .115v @ idle, you needed a new one anyway.
I'm sure the MAP sensor was bad, but I'm disapointed that it wasn't the "cure all" - thanks for the encouragement.


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You have no other choice now except to get a good scan of all PCM inputs & outputs. You have to know how the PCM is interrupting sensor inputs.
Should they be able to give me a printout? That way I can give you the results.

So far so good. no new SES lights. The car sounds good. When we started it back up after changing the ETC and MAP sensor I let it idle quite a long time and ran the scanner on it. I was watching the RPM'* hoping they would go down. I noticed that the RPMS were like 850 in idle in park. After the engine was good and warm I had my son pull it down into drive and it read like 670 RPM'*. Whats funny is the tach on the dash read 1000 rpms and 800 RPM'* respectivly. At this point, I'm going to let him drive it for a few days see if it throws any ses lights, and schedule a full scan after the new year. I'll report back if anything happens. BTW, the hard starting seems to be fixed. I think the ETC sensor was indeed bad. Tomorrow morning will be the tell tell test for that

Thanks again for all your help
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Old 12-30-2007, 09:07 PM   #25
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Quote:
Originally Posted by BMWhound
Should they be able to give me a printout? That way I can give you the results.
Most full function scanners can give a freeze frame print-out or “data log”, however, not all shops have the correct USB or Serial Interface cable for downloading data from their scanner to a printer. Ask this question before you commit to the service.

It is not uncommon for the IC tach to not be in tune with a scanner reading. I would much rather trust the scanner rpm. Remember, anytime you change sensors, disconnect battery cables, delete codes & erase PCM driving parameters, the driving parameters need to be “relearned” while driving. The PCM can take 150-250 miles to relearn and feel comfortable, depending on driving style.

When at idle and in gear, does the car pull & gain mph with your foot off the brake? Some pull is normal, however, you don’t want it to accelerate like you have your foot on the throttle.
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Old 12-30-2007, 09:53 PM   #26
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When at idle and in gear, does the car pull & gain mph with your foot off the brake? Some pull is normal, however, you don’t want it to accelerate like you have your foot on the throttle.
No - It drives very nice actually. It wont take my son very long to get the 200 miles on it. His girlfriend lives 10 miles away :P I've got all new battery cables (positive) coming from Rock Auto to put on too. I cut the original connectors off shortly after I purchased the car and put on some after market connectors. When we were doing the UIM/LIM repair I noticed how bad the cable was corroded where its clamped on the connector. I don't think it'* real bad, but I might as well replace this stuff too.

What can I expect to pay for the full scan ?
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Old 12-30-2007, 10:15 PM   #27
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It wont take my son very long to get the 200 miles on it. His girlfriend lives 10 miles away
Yea, I know what you mean here; son with a grilfriend 10 miles away = 50+ miles a day!
Quote:
I've got all new battery cables (positive) coming from Rock Auto to put on too. I cut the original connectors off shortly after I purchased the car and put on some after market connectors. When we were doing the UIM/LIM repair I noticed how bad the cable was corroded where its clamped on the connector. I don't think it'* real bad, but I might as well replace this stuff too.
I found a permanent fix for the terminal dilemma on all my GM cars by replacing the terminals with heavy duty soldered terminals and gold plated battery post. Never had a problem since!


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What can I expect to pay for the full scan ?
Depends on the shop, dealer runs 85-100 bucks, some independent ASE shops may charge 65-85 bucks. What'* important, wherever you take it, be sure they know what they are doing! I would rather pay someone knowledgeable 100 bucks, than some gobber (parts changer) 50 bucks. Like everything else, you get what you pay for!
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Old 01-01-2008, 08:02 PM   #28
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Day Two - The hard starting problem is fixed. Car starts right away now. No ses lights either. Keeping my fingers crossed. New Battery cables will be in tomorrow and I'll get those on too.

Z, like those battery terminals man. Nice idea.
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Old 01-01-2008, 09:58 PM   #29
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Quote:
Originally Posted by BMWhound
Day Two - The hard starting problem is fixed. Car starts right away now. No ses lights either. Keeping my fingers crossed. New Battery cables will be in tomorrow and I'll get those on too.

Z, like those battery terminals man. Nice idea.
Thanks for the feedback! Your troubleshooting persistence was the key to success here!
Many people do not follow iinstructions, or provide feedback as well as you have. Keep us posted on any new developments and may the Bonnie provide you with many more miles of happy motoring! BTW, when you change the battery cables, don't forget to disconnect the negative (-) cable first!
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Old 01-01-2008, 10:54 PM   #30
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Quote:
Originally Posted by HotZ28
Thanks for the feedback! Your troubleshooting persistence was the key to success here!
Many people do not follow iinstructions, or provide feedback as well as you have. Keep us posted on any new developments and may the Bonnie provide you with many more miles of happy motoring! BTW, when you change the battery cables, don't forget to disconnect the negative (-) cable first!
Thanks. I'm to stubborn to give up :P

Curious...why should I disconnect neg cable first? Sparking from the + terminal bad for electronics/computer?
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