LQ1 Surging

[Z34guy]

I just remembered the Monte doing this, but nothing was wrong when I pulled it into the shop and checked it out.

I'd be driving along normally and then notice the car idling rather high. Came to a stoplight, where it was idling at 1950 RPM. At the stoplight, I put it in park, which somehow cause the RPMs to shoot up to 4,000. Restarted the car and all was well. The car's done it twice on me, about a month and a half apart between incidents. Any ideas as to what could be the cause? Like I said, the car's only done it twice and a massive time frame between incidents.

[Leo090]

This is a very common problem amongst many gm engines. I experience it with my 97 lumina and others on this site also complain. An intermittent problem of rpms changing mid drive then a restart fixes it. A mechanic will suggest a multiple amount of errors from IAC, TPS, MAP, MAF, 02 sensors, fuel filters, spark plugs and wires. Gasket leaks , Vaccuum leakes, Stuck throttle, stuck egr. All can cause this.

 

I just turn my car off and on when nearest safe possibility arises and usually have another 1-2 hours of driving without the problem.

[Galaxie500XL]

I've had this happen twice with my '95 LQ1. In both cases, it was a bad throttle position sensor...the first replacement lasted less than 3 months!

 

The second has been on the car for nearly a year now, with no further problems. Checking with a scantool, when the car was misbehaving, the ECM believed the throttle was open 14% when it was actually closed. On restarts, it would frequently show a correct %.

[Schurkey]

I just turn my car off and on when nearest safe possibility arises and usually have another 1-2 hours of driving without the problem.

You'd let the engine fast-idle out of your control, and you're satisfied with a band-aid solution that lasts TWO HOURS?

 

Do NOT drive behind ME with an engine you can't throttle back. You're asking for a collision and a lawsuit.

[Psych0matt]

You'd let the engine fast-idle out of your control, and you're satisfied with a band-aid solution that lasts TWO HOURS?

 

Do NOT drive behind ME with an engine you can't throttle back. You're asking for a collision and a lawsuit.

 

 

I dont understand your logic? How does the engine idling high have anything to do with safety? I'm having issues with my GTP until it warms up, and aside from it being louder from having higher RPMs I don't have any issues. The break pedal still stops the car when you push it (well, in a first gen that's another thread for another day )

[Schurkey]

Braking distances greatly increased from brakes having to fight engine power due to high idle speed.

[Leo090]

OK yes, braking distance might increase slightly, but I am completely aware once my rpms start reving higher, I can feel it in the car, thus I account for it with further distances between cars and I brake heavier. I do agree that i would rather drive without this issue, but since it can be a number of things I do not want to spend all my wallet especially when i feel i have FULL control of the vehicle, its just a nuisance.

 

 

 

Also replying to earlier posts, How do you know you fixed the problem, just because it didnt come back for a year? I have times when this problem disappears on its own for a year, usually over the course of the winter months it will behave well. I think your issue was not your TPS, your tps might have acted up as a result of something else being wrong in the car.

[Z34guy]

A mechanic will suggest a multiple amount of errors from IAC, TPS, MAP, MAF, 02 sensors, fuel filters, spark plugs and wires. Gasket leaks , Vaccuum leakes, Stuck throttle, stuck egr.

The only one of those I haven't checked is the TPS. My teacher's a GM Mastertech and said I wouldn't catch it unless it happened again while checking it out. And as with the temperamental V6, it's never done this when it's in the shop. Typical. Like I said, It's only happened twice, with massive amounts of time between incidents, so I'm not overly worried about it. I just figured the forum would have some insight into this strange issue.

[Leo090]

Take my advice and dont bother changing worrying about it until it happens daily and is really getting on your nerves.

 

It used to happen daily to me a few summers ago, then it just went away. I changed my fuel filter before this summer and I only had the issue twice.

[Psych0matt]

Take my advice and dont bother changing worrying about it until it happens daily and is really getting on your nerves.

 

As much as I don't think it's a huge issue at the moment, this is the worst advice I've ever heard. Yes, lets wait until we're stranded because we didn't bother checking into something that's probably a cheap and easy fix.

 

(Disclaimer: I'm not saying I've never done this, just saying it's not good advice)

[Z34guy]

When I'm able to catch it and diagnose it, I do plan on fixing it.

[Leo090]

As much as I don't think it's a huge issue at the moment, this is the worst advice I've ever heard. Yes, lets wait until we're stranded because we didn't bother checking into something that's probably a cheap and easy fix.

 

(Disclaimer: I'm not saying I've never done this, just saying it's not good advice)

 

I would not recommend this advice for every issue. But for his particular intermittent issue he should not be worried. I have never heard of a FULL 100% diagnosis and fix for this issue anywhere on the internet. I have never heard of anyone being stranded because of this issue. It would become more of a noticable problem waaay before he gets stranded. A simple restart fixes the issue and may disappear for a while.

Why tear apart your wallet and your engine only to find out you still have the problem and are $700 short because you bought new sensors when yours were perfectly good. Obviously if you feel you have no control of the vehicle and do not feel safe, then sure go to a mechanic and find a fix. But if you know its just a nuisance, you'll be okay.

[Psych0matt]

Oh I agree that it's probably not something to be too worried about, but I'm just saying that it's probably not something one should just ignore completely either.

[Galaxie500XL]

Leo;

 

That's why I used the scantool. Once I could see what the ECM was seeing, it made sense WHY the engine was behaving that way.

 

...and while I agree the problem MAY return..I'd think after a YEAR, it's probably safe to assume I fixed the problem---considering I drive the car daily, it's had plenty of chances to mess up.

 

OK yes, braking distance might increase slightly, but I am completely aware once my rpms start reving higher, I can feel it in the car, thus I account for it with further distances between cars and I brake heavier. I do agree that i would rather drive without this issue, but since it can be a number of things I do not want to spend all my wallet especially when i feel i have FULL control of the vehicle, its just a nuisance.

 

 

 

Also replying to earlier posts, How do you know you fixed the problem, just because it didnt come back for a year? I have times when this problem disappears on its own for a year, usually over the course of the winter months it will behave well. I think your issue was not your TPS, your tps might have acted up as a result of something else being wrong in the car.

[GP1138]

I would not recommend this advice for every issue. But for his particular intermittent issue he should not be worried. I have never heard of a FULL 100% diagnosis and fix for this issue anywhere on the internet. I have never heard of anyone being stranded because of this issue. It would become more of a noticable problem waaay before he gets stranded. A simple restart fixes the issue and may disappear for a while.

Why tear apart your wallet and your engine only to find out you still have the problem and are $700 short because you bought new sensors when yours were perfectly good. Obviously if you feel you have no control of the vehicle and do not feel safe, then sure go to a mechanic and find a fix. But if you know its just a nuisance, you'll be okay.

 

Leo, this forum has been around for awhile, and there are many people here who have had this issue and have fixed it. I owned several LQ1 cars that did NOT do this, and when they did I was able to narrow the issue down without spending hundreds of dollars on sensors. There are cheap/free ways of dealing with this problem. An engine idling up to 4k RPM is NOT normal, and at the wrong time it could indeed result in a collision.

 

Trust me, nobody here is going to spend upwards of $700 on sensors, anyway. We all have junkyards we go to and people on here that have spare sensors are often willing to sell them cheap.

 

In this case, I'd clean the IAC first.

[mfewtrail]

Z34: What have you checked on the car so far and what did you check it with?

[Z34guy]

Z34: What have you checked on the car so far and what did you check it with?

trying to remember. Forgive me if I miss a few.

I checked the fuel pressure with a fuel pressure gauge on the initial thought it could've been the pump or filter, which was fine, checked the IAC that didn't need cleaning, went over most of the sensers with a digital multi-meter and everything was fine, and even looked it over with a Snap On Modus scan-tool. I couldn't find anything wrong. It's baffling. I suppose I won't know what's wrong until it misbehaves while I'm checking it out. It wasn't misbehaving during my checks...

[95LQ1VERT]

I will ressurrect this thread to help with my problem I have been dealing with lately.

 

I am having the same problem with the idle as the OP had been dealing with, but mine is frequent. Like everytime I drive Frequent... So far I have cleaned the TB and all ports inside, replaced the intake gaskets, bought a new IAC valve and it made it worse so I unhooked the battery, unplugged the IAC valve, rehooked the battery, started it and then adjusted the idle screw, which did bring the idle in park down to 900-1000 rpm, but after driving it a few miles (warm or cold) it will seem as if the car is trying to run away. It idles in drive around 1250- 1400 rpms and then when it goes into park its anywhere from 2400 - rev limiter.

 

My next part to throw at it was going to be a new TPS, which I seen was the culprit for a few.

 

1.) What is the process and tools needed to test the voltage going to the tps? (never have done such work)

2.) Or would it be smarter to just go buy the new tps and replace it?

 

Need to know ASAP, I need to get tires for my car before winter, I dont want to drive a car that could be a runaway Toyota:burnout:, in snow, without tires!!! HAHA

[AL]

Possibly intake gaskets^^

[95LQ1VERT]

I literally just did them 2 weeks ago.

[Galaxie500XL]

I used a scantool to diagnose mine...TPS voltage and Throttle% shows on my tool...in the case of mine, sometimes when the throttle was closed, the computer thought the throttle was actally open around 6-9%...at other times, it read correctly.

[Schurkey]

2.) Or would it be smarter to just go buy the new tps and replace it?

Diagnose first, replace/adjust later.

 

By the time you're done throwing parts at it, you could have paid for a proper diagnosis and repair. Or you could have paid for a REAL scan tool and a proper repair.

[95LQ1VERT]

My impatience got the best of me so I said the hell with it and I went bought the part and put it in. That and I was bored.

 

To my surprise though, after replacing it, I havent seen any absurd behavior from it. Yet atleast.

 

Also I have been searching for a code scanner like yours Galaxie500XL, the Actron CP-9110, and I havent found 1, even ebay doesn't have em'!

[RobertISaar]

the TPS issue can be caused by a few issues, mostly if there is a significant drop in system voltage when cranking, the 5V reference circuit will actually drop voltage as well, causing the read TPS voltage to drop and the TPS % value is created based off of the false lower voltage.

 

of course, a bad TPS will calso cause issues when cranking or otherwise.

 

a good(read, actual, not a "blink causing") scantool/aldl cable will show TPS%, and if you're seeing anything other than 0.00 or 0.39% with a closed throttle, it's a dead giveaway that the TPS is either misadjusted or the computer has a bad value stored. alternatively, you could potentially "fix" the issue by reseting the PCM's NVRAM by removing the +12V used to store it's key-off values.

[Galaxie500XL]

http://www.ebay.com/itm/SCANTOOL-SUNPRO-ACTRON-CP-9110-/251173923717?pt=LH_DefaultDomain_0&hash=item3a7b21eb85

 

 

See if that works...

 

EDIT: Never mind...seller reports the display has issues...and I noticed the cable is missing...but it DOES seem to have the '84-'95 GM cartridge...at least you know what it looks like...

Edited October 27, 2012 by Galaxie500XL