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2001 Cadillac Deville
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14 Posts
Discussion Starter · #1 · (Edited)
Hello all,

I posted three months ago with starting problems that - thanks to your suggestions - were basically resolved by TB and IAC valve cleaning.

Now on to the problem that existed before but is getting worse now: Sometimes our 2001 Deville accelerates on its own. Yesterday, after a few short stops at the mall, I entered the highway uphill with up to 3,000 rpm. From there, he almost drove by itself at about 50 mph and 1,500 rpm. As soon as I was applying the breaks to exit the highway after a minute or two, the rpm would go slightly up, about 100 rpm. Foot off the brake, 100 rpm less. I had to force the car to stop. Standing still, rpm were at about 1,200. After I yanked the transmission into neutral, it rose to 2,000 rpm. While still in neutral, I applied the accelerator, and the idle rose to 3,000 rpm and stuck there. Then, after turning the car off, removing the ignition key and restarting after about half a minute, he was back to idle at about 750 rpm.

This is the worst example of the problem, but I can feel him accelerating ever so slightly from time to time.

The codes from today (all history):

IRC U1016 - Loss of Class 2 Communication with VCM / Loss of Communications with PCM
PCM P0507 - Idle Speed High
PCM P1189 - Engine Oil Pressure (EOP) Switch Circuit

My hunch - not based on actual knowledge, but on reading a related post here - is that the TPS is to blame. I checked the floor mat and don't think its messing with the accelerator.

So what steps could I take to address this issue? Do I have to unscrew some plastic near the accelerator to check if some cable is loose?

This may be unlikely, but can the problems with the idle I had weeks ago contribute to the acceleration problem? Again, the car's starting all the time. However, in the morning when cold, he only idles at somewhere between 600 and 700 rpm. If I then drive just a minute and stop for another, afterwards he's at 1,200 rpm (where I expect him to be cold), moving down gradually. My idea was that I should just clean the IAC valve again and more properly, but maybe this is also contributing to the unvoluntary acceleration problem.

Edit: Something I also noticed when the acceleration phenomenon was happening, that when I roll downhill with the transmission in neutral, the idle will rise in lockstep with speed. Does that point to some problem?

Any help is highly appreciated! Thanks so much in advance!

Hadema
 

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2001 Cadillac Deville
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14 Posts
Discussion Starter · #2 ·

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2003 DTS
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46 Posts
my car kept stalling & having the low idle at first. I tried cleaning it an that worked temporarily. Then it starting idleing very high (3000rpm) at stop signs or in the drive way. I ended up buying a new one for around $195 & installed it myself.
 

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2001 Cadillac Deville
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14 Posts
Discussion Starter · #4 ·
my car kept stalling & having the low idle at first. I tried cleaning it an that worked temporarily. Then it starting idleing very high (3000rpm) at stop signs or in the drive way. I ended up buying a new one for around $195 & installed it myself.
Numbamane, I understand you mean you replaced the IAC valve and that solved all these problems?

Perhaps any recommendations on the replacement, anyone? Rockauto carries an AC Delco IAC Valve for $211. Is that OK, or should I go with a different manufacturer?

Thanks!

Hadema
 

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2003 DTS
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46 Posts
yes when i replaced the iac valve it solved my low idle, high idle & stalling problems. but 2 weeks prior while i was in the wurkin area i cleaned my throttle body(TB CLEANER), Iac valve(ELECTRIC PARTS CLEANER) & maf sensor(MAF CLEANER). Replaced the map sensor too. I was still having the high idle code PCM P0507. So i just replaced the iac valve with a new one i bought from amazon.com
$196 with free shipping. took 2days to receive it.
 

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2001 Cadillac Deville
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14 Posts
Discussion Starter · #6 ·
Appreciate it, Numbamane.

Would anybody else like to weigh in on this? Ranger, submariner409? Is the IAC valve the most likely culprit or could it be some TPS-related issue? I would love to hear a second opinion on this before I spend $200 on a new IAC valve.

Thanks again!

Hadema
 

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2008 Cadillac DTS 4dr Sdn w/1SE
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57 Posts
When I had the same acceleration problem a few months ago , it turned out to be the plenum was cracked. I replaced it and no problem since. I didn't have the same codes but had the same symptoms. I also cleaned the aic and tb first but it still would happen just the same as yours. there's a thread about replacing and the parts are about $40. http://www.cadillacforums.com/forum...-northstar-plenum-duct-replacement-steps.html
 

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2010 DTS
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87,955 Posts
I had thought about mentioning the plenum, but didn't because you had no lean trim codes. It would be worth checking out though since it is so easy. IAC valves don't fail very often and should set a DTC, but it would not hurt to pull, inspect and clean it before replacing it. Also clean the TB if you haven't already.
 

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2001 Cadillac Deville
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14 Posts
Discussion Starter · #9 ·
Thanks for the input, randythemachine and Ranger!

TB was cleaned during the regular inspection in January (properly, I hope), and I couldn't detect a crack in the plenum when I checked after the problem appeared first a couple of months ago.

Now, since I didn't have any problems for a few weeks after I cleaned the IAC valve a little bit in early January, but things are gradually getting worse again, and since no one suspects some other thing such as the TPS to be to blame, I went with the original suggestion to replace the IAC. I should get it tomorrow or on Saturday. I'll keep you posted.

Thanks again to all who replied so far!

Hadema
 

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2001 Cadillac Deville
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Discussion Starter · #10 ·
Just as follow-up: Replacing the IAC valve solved the problem, just like in Numbamane's case.

In case you happen to drop the screws that hold the IAC valve in place, their specification is M4-.7 metric, available in any larger hardware store.

Hadema
 

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2001 Deville DHS (RIP) 2005 Cadillac Escalade
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Hey Hadema and guys,

I have a question or two for you Hadema.

Before you changed you IAC was your check engine light on?

If so, when you did, did it cut the check engine light off??

And How's your Cadi been riding since you changed the IAC? Any more related codes??
 

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2002.5 F55 CORSA STS, 2014 Explorer XLT FWD
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