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Loping Idle with P0171 and P0174 codes


basod2002

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Gentlemen,

My '01 STS has been giving me fits as of late. Started with an erratic idle when I pulled in the garage 2 weeks ago. The next morning at the one stop light on my way to work the SES light came on and idle was loping ~200rpm. Codes came back as 0171 and 0174 lean bank 1 and 2. I replaced the MAF and found no improvement. So I returned the part, and went on troubleshooting after I learned how to check my codes through the info center. I removed the intake duct and examined for cracks. Also inspected the silencer (heard those can develop weld cracks). Checked all vacuum hoses for obvious cracks, Cleaned PCV, checked FPR, replaced fuel filter w/injector cleaner - none helped. I decided to remove the IAC plug with engine idling, and loping immediately stopped. I've replaced the IAC ($240) and the codes continue to appear, with loping idle. I read an intersting bulletin on Borg-Warner website about alternator regulators failing causing idling symptoms. I tested main output to chassis ground and found ~ 7-8 milli Volts of AC power. The website said 2 volts would cause PCM to compensate for false electrical load. I went this route because I noticed a dimming of interior lights while the car was idling rough. I've read some other posts with similar symptoms and plan on removing the Throttle body/inspecting inner boot to intake, but I'm curious why the gentleman that posted it said he needed to remove the intake to get to the boot, or did he just mean the TB?

Thanks,

Steve

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first thing hopefully everything is stock no add on gizmo's.

Try this old easy trick....using carb or brake cleaner spray suspected vacuum leak areas , That Tb connection, vacuum lines, intake manifold etc......A change in rpm will indicate a likely vacuum leak, in your case it may momentarrly smooth out as the area is sprayed..

have to add the spray needs to be flamable avoid the newer eco friendly.

PS did unpluging the IAC cause a code to set??

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Yes, carb or brake cleaner will find the leak.

On my 2001, it developed a leak in the narrow rubber boot located between the intake manifold and the throttle body 'plate' assembly. About a $15 part. The intake needs to come off to replace the boot.

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I wasn't sure if carb/brake cleaner was a good thing to spray on the "plastic" intake manifold. I'll try it out tonight. I'm just curious though as to why the intake needs to be removed to get at that boot. I figured the Throttle body could be removed and boot replaced that way. But I'm very appreciative of all the help.

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Of yeah I don't beleive unplugging the IAC caused a new code, but I could be wrong. I unplugged it after I had become frustrated after the new MAF did not solve the problem and reset my codes. The idle seems a lot smoother today, but the codes are staying current now, I think the PCM has reprogrammed itself to compensate for everything I've toyed with to date. I still havea PDM code that I haven't checked in my book, sorry don't have it right now, but think its from having passenger door glass replaced last fall - hole different ball of wax. Interesting note though, if glass is replaced and auto up-down function is on the fritz (rolling window down after going closed) Unplug the driver side window module and it should reset window locations. Took the shop 3 times and the guy did it by accident, he started working on drivers side window, after work order ticket was incorrectly written for that module. Needless to say thats why I'm trying to fix this issue myself, don't have much faith in the local caddy dealership service department here.

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I am not talking about the MAF hose..

In between the intake and the throttle body crossover there is a 6 inch x 1 inch rubber coupler hose. These can develop a crack in the rubber and leak causing the problem you describe. The intake has to come off to replace this hose.

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I am not talking about the MAF hose..

In between the intake and the throttle body crossover there is a 6 inch x 1 inch rubber coupler hose. These can develop a crack in the rubber and leak causing the problem you describe. The intake has to come off to replace this hose.

I appologize I thought you were saying the intake manifold needed to be removed.

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I've found the vacuum leak on my STS, the same one Logan had found crack in, between T/B backer plate and intake manifold. Where can I find this part? Does anyone have any input on intake manifold gaskets, Felpro/OEM. Thanks guys

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I've found the vacuum leak on my STS, the same one Logan had found crack in, between T/B backer plate and intake manifold. Where can I find this part? Does anyone have any input on intake manifold gaskets, Felpro/OEM. Thanks guys

I would go to the dealer to get the part. You can't go wrong with OEM parts, try gmotors.com or rockauto.com for good prices

Pre-1995 - DTC codes OBD1  >>

1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm

How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/

Cadillac History & Specifications Year by Year  http://www.motorera.com/cadillac/index.htm

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I am not talking about the MAF hose..

In between the intake and the throttle body crossover there is a 6 inch x 1 inch rubber coupler hose. These can develop a crack in the rubber and leak causing the problem you describe. The intake has to come off to replace this hose.

I appologize I thought you were saying the intake manifold needed to be removed.

$15 part at dealer. The intake does have to come off to replace it.

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I've found the vacuum leak on my STS, the same one Logan had found crack in, between T/B backer plate and intake manifold. Where can I find this part? Does anyone have any input on intake manifold gaskets, Felpro/OEM. Thanks guys

I would go to the dealer to get the part. You can't go wrong with OEM parts, try gmotors.com or rockauto.com for good prices

Yeah upon further inspection last night I realized the intake does have to come off (Coolant crossover clearance is too tight). I'm having trouble with the part number or description nothing seems to match. I'll try the local dealership on monday if no luck online.

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Replaced the intake boot, and found suspected tear as did Logan. The parts counter at the dealership didn't even have to look up the number, seems he gets these off the shelf quite often- he says. Easy fix though, wish I had asked about draining the coolant, I didn't think it passed through the intake manifold, but drained it anyways per shop manual (messy waste of 2 hours). Job would've taken less than 2 hours had I not also broke a throttle body bolt (was looking at the torque value of 98 and earlier models-168in-lbs vs. 106in-lbs, good ole Lowes had some 6mm bolts that will do for now. Thanks for the help gentlemen.

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Glad you got it all fixed. I merged these threads/topics together so that the whole story is in one thread. This helps future readers who might have the same issue.

Bruce

2016 Cadillac ATS-V gray/black

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