stall on traffic ( low RPM ) and have hesitations

[anxxus]

Hi guys!

I`m new on this forum and I will like to understand what going on with my car (Pontiac Grand prix GT 2001). I`m pulling out all of my hair lol

I`m sure someone already have those symptoms with their cars and found the problem ! I really like my car but now it make me wonder about GM !

Symptoms :
- Car wants to stall on traffic (low RPM) and have hesitation on acceleration most when going on second gear, most of hesitation in hot condition.

What I did so far:

I clean the MAF sensor, Recheck all the vacuum line, Change air filter, Recheck all wiring, Check and clean all ground lugs, clean butterfly valve on throttle body, and clean IAT sensor.

Once everything done I went for a small spin, I notice I awaken a monster in my car.
The car feel having a turbo engine, I really felt the difference in performance and acceration.

I left my car running at idle (warm) for a few minutes but the car still wanted to stall but every time it regain (RPM) never stall until now.

I notice my IAC valve end was dirty so I clean it. But how do I know if the small servomotor will retract the small rod? it seems to me that the length is always the same?


Anyway could it be the IAC valve was faulty? How do I test it ?
Give me some Tips I ran out of ideas here!
Regards

[Liquifire]

Does it idle OK...if the IAC is not working correctly your car will idle not smoothly at all or may not even run. If this is the case and you can make it idle good with the gas pedal, then your IAC is no good. Do you have any codes or SES lights or whatever?

[anxxus]

Hi there!
Thanks for the reply

For your information’s I do not have any check light! No OBD II code reading for what I remember!

Since I thought the problem was the IAC .I went to buy this morning a new IAC sensor and plug it in at the nearest CARQUEST (Very cheap part).
I left it over for a awhile and notice that the RPM stay fluctuate around 1000RPM / 1100RPM ( engine cold ) and then fluctuate around 750RPM/850RPM) Hot engine.
Everything seems fine for me until the car stall gain after 12/15 minute on idle.

I went for a spin around the block and bang !! Hesitation and stalling issue appear again! Nothing was change. No improvement, nada!

- One thing for sure I think first of all that the hesitation and the stalling issue are link and a faulty sensor is responsible for it!

- It must be electrical problems 99.99% sure!

- It cannot be a Fuel Pump issue whatover because the pressure is just fine and you can easily hear the fuel pump doing the job. Even if the fuel pump was faulty the car won’t even start!!!!

- All the cleaning I did on the throttle body improves the acceleration, that way I felt having a turbo!

- I don’t think its a faulty vacuum line, everything seems in theory correct. Even if it was a line I be very surprise!

- Wirings, alternator, battery, coil pack, spark plugs , TPS, MAF, IAT, are will not cause this issue! Cars will run like a crap! and probleably a check engine light will appear !mine runs smooth.

It could be one of those items

- Cleaning Fuel Injector
-EGR
-o2 sensor
-bad ground
-bad ECM
-Faulty wires (Which one only Gods know )

I decide enough puzzling with this car I left to the shop. They will problebly put a diagnostic scanner/computer.

In meantime if someone could point me in a good direction
It will be very appreciated!

Regards!
Someone that lost faith in GM!
VR

[Liquifire]

unfortunately, it could be lots of things as you have pointed out. Just going by the frequency of failure rate, I would guess a MAF sensor as these go out all the time. But, if you have no reason(codes or lights) to suspect the maf, then I would start with the cheapest things and work my way up unless I found something concrete. The next time it starts acting up, unplug the MAF and see how it runs then. If it improves you have probably found your problem. If not...I was no help. Good luck, you will probably need it.

[GPdude97]

This might sound dumb to a few people on here but check your plugs, wires, and the ignition coils. I have the same exact problem with my car and it got so bad one night it threw an SES light at me. I went to Autozone to get the code as I do not have my own scanner and it said that cylinder 4 was misfiring. It only happens when the engine is hot. I am replacing the plugs and wires first and then if thats not it then I will replace the ignition coils. Let me know what the problem was when you find out.

[anxxus]

Today
The shop call me with a interesting news concerning my issue.
They told me it could be one of the following

90% a faulty CPS ( Crank positioning sensor ) 240$ Can
10% a faulty TPS ( throtle postioning sensor )

What do you think !!!!

[TheOtherNick]

Well they should be able to see what percent the tps is showing on a scan tool and be able to see if that is your problem. I would try unplugging the maf to see it runs any different.

[anxxus]

I already try to unhplug the Maf, Cars runs like crap and Check engine light went on . Put back everything and car runs fine.
So i deduct that Maf Sensor was not faulty.
Hesitiation on accelaration and stalling while idling was still present thought !

After my research and goggleling all over the net tonight everything is pointing towards a faulty CPS ( crank postioning sensor )

[Liquifire]

CPS is very often the culprit on our cars as well....vacuum leaks, MAF, and CPS I would say are the problem on 80% of all issues described on here. It is a fair possibility, but usually the cps causes the car to just quit altogether, not run funny. It usually runs or it doesnt. I guess it could be as good as a guess as any.

[anxxus]

By the way

What the life span of a CPS ?

I'm curious !

[Liquifire]

no way to tell...some fail soon some go 200k
anyones guess
just like any other sensor

[Liquifire]

did you end up replacing the cps yet???

[anxxus]

Well my there dear friend here is my story.
After running between shop and dealer Last Friday I toke a radical decision about the faith of this car.
Apparently the stalling issue was a faulty CPS cost me about 350 (labor and parts) and problem still occur when engine was warm. They couldn’t find the accurate faulty part, and the shop mentioned to me that the hesitation problem was probably a faulty transmission. So I decide to have another opinion somewhere else . Tranny shop told me it could be a torque converter in the tranny was faulty and they should take a part the tranny to see and rebuilt the tranny cost estimated about 1400 $ plus labour !
dealerships have been unable to duplicate since it is extremely intermittent.
A lot of of people all over the net are having this kind of issue, but no accurate answers to the problems.
I said enough was enough I could take it anymore about this . So I decide to sell before it was too late and now its no more my problem I feel free thought ! I`m now fed up about GM and I`m going to buy my next car Japanesse

Regards,
Vito

[asager]

I am having the exact same problem with my 2000 Grand Prix GT. I've done the same, replaced the plugs, wires, and fuel filter. I've also had the fuel system cleaned as well as fan fuel injector cleaner through the gas tank before and after the cleaning.

Could this be a problem with the fuel pump itself? From what I've read, it doesn't sound like a fuel pump problem would cause these symptoms, but like you, I've run out of things to check. What about the ECU "electrical control unit" or a sensor (throttle position sensor or O2 sensor)?

I only have 100,000 miles on it and would love to keep it another 3-4 years.

Any suggestions??

[MrTube]

Good luck with a japanese transmission anxxus. We are the proud owners of a Honda J-35 with its famous Honda 5 speed automatic trans and I wish I wasn't. Burnt fluid by 20-30K is common.

Known for failing constantly in Hondas and Acuras. Google "honda transmission" and see what comes up. Torque converters fail very often and cost the owner $2-4K to have replaced. There was even a class action lawsuit on Honda regarding it I believe in 2004.

Toyotas are not much better.

[anxxus]

Well Mr. Tube only find commerce that sell Transmission on Honda/Acura (acura transmission - Recherche Google=) no problems regarding this.
Anyway assager last news concerning my old cars is still sitting at the dealer.
I really wanted to keep that car for at least 3 years like you but destiny decide otherwise. I`m sure the problem was the ECU.
Give a feddback if you find a solution i`m curious.