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Weird problem

19K views 86 replies 17 participants last post by  TulsaVic 
#1 ·
So on Thursday morning I was heading to get mt car state inspected. It started running strange almost like it is misfiring. The car is not throwing any codes. When at a stop light the car seemed to want to go. It was lurching forward even though my foot was firmly on the brakes and the throttle was closed. This same thing happened to my '02 Seville and it was the intake plenum. So yesterday I went by the dealer and picked up a plenum. This morning I removed the intake manifold to find the plenum in good condition. No tears and seemed to snug up nicely. So I figure it might be a cracked spark plug as that has happened to this car once before. So I change out all 8 spark plugs with AC Delco 41-987's. Problem is still there. Then I decided to clean the throttle body as I had cleaner within arms reach. The problem is still there.

Since I am not getting any codes I am at a loss as to where to check next. Does anyone have any ideas? I could start throwing parts at this thing and eventually I will get it fixed. But that will be expensive. Any input is greatly appreciated

Don
 
#5 ·
This is definitely an engine issue not a brake issue. I did check the vacuum hose for cracks and didn't feel any

Don

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That sounds like the throttle position sensor. What are your rpms at idle? What happens if you put it in neutral, foot off the gas? When the TPS went bad on my DeVille, the rpms would jump up to 2000 in neutral.
Idle stays fairly steady. If the car is in park or neutral no noticeable change in RPM but you can feel the "stumble". I just wish a code would set already so I know where to look. I think I may just throw a MAP sensor in there and see how that does. Not sure that will do anything but they are pretty cheap

Don
 
#3 ·
A little more info. I drove the car to the store and the engine got fully up to temperature. Once up to temp the problem seems to go away. That is what lead me to believe it may be a cracked spark plug. But when I pulled out the plugs none of the insulators had cracks.

Don
 
#7 ·
#PIP3146D: Rough Idle Crank No Start Extended Crank Or Misfire When Cold Due To Sticking Valves Or Excessive Carbon On Top Of The Valves - (May 11, 2011)
Subject:
Rough Idle Crank No Start Extended Crank Or Misfire When Cold Due To Sticking Valves or excessive carbon on top of the valves

Models:
2000-2012 All Passenger Cars with Gasoline Engines
2000-2012 All Light Duty Trucks with Gasoline Engines


[HR][/HR]This PI was superseded to update recommended field, model years and engine list. Please discard PIP3146C.
[HR][/HR]The following diagnosis might be helpful if the vehicle exhibits the symptom(s) described in this PI.
Condition/Concern:Rough idle, misfires, extended crank, or crank no start when cold. The engine may run rough for up to 5 minutes after starting the engine and may exhibit a P0300 DTC too. This may be caused by sticking valves or excess carbon due to fuel contamination
Note: fuel oxidation and volatility concerns can often cause these issues as well, however they cannot generally be checked in service. Trying a different, high quality fuel is sometimes the best diagnostic.

When the engine is cold, the compression on multiple cylinders may be at 0 PSI. The engine also may pop through the intake or exhaust while cranking and the spark plugs may be fuel fouled when inspected. Some engines may also experience valve damage or cam followers that are out of position as a result of this.
This condition can occur in specific areas of the country for a period of time and then it will no longer occur after the suspect fuel source has been consumed in that area of the country.
Recommendation/Instructions:If the SI Diagnosis leads to a compression loss due to sticking valves, the following information may help:
If there is no sign of valve damage or cam followers that are out of place, perform the following procedure to free up sticking valves and to prevent the valves from sticking again. If valve damage is present or if there are cam followers that are out of place, perform engine mechanical repairs as necessary to correct the concern and then perform the procedure below to prevent the valves from sticking again.
  • Clean the fuel system by following the applicable "Fuel System Cleaning" procedure outlined in SI.
  • Add fuel injector cleaner "GM Fuel System Treatment PLUS, P/N 88861011 (for U.S. ACDelco, use 88861013) (in Canada, 88861012)"... see This PI was superseded to update recommended field, model years and engine list. Please discard PIP3146C. bulletin # 05-00-89-078B, to the fuel tank in the approved quantities.
  • Refill the fuel tank using fuel from a high volume, high quality filling station.
  • Clean the induction system using GM Top Engine Cleaner. Follow the directions on the can but DO NOT force the engine to stall since forcing the engine to stall with liquid Top Engine Cleaner could cause the engine to hydro-lock. * If available use an atomizer with Top Engine Cleaner through the throttle body.
  • Advise the customer to change fuel filling stations. They should use fuel from only high volume, high quality filling stations or they should use a Top Tier Detergent Gasoline if available. See 04-06-04-047I (U.S.) or 05-06-04-022G (Canada) for details regarding Top Tier Detergent Gasolines.
 
#11 ·
So impossible they wrote a PIP about it, whatever that stands for. Gas will go bad if it sits for months, just ask my lawnmower. That's one reason they recommend high-volume stations.

I was asking a general question about octane. I can't detect any difference. I'm wondering if anyone else does.
 
#12 ·
So impossible they wrote a PIP about it, whatever that stands for. Gas will go bad if it sits for months, just ask my lawnmower. That's one reason they recommend high-volume stations.

I was asking a general question about octane. I can't detect any difference. I'm wondering if anyone else does.
Speaking only for myself and my car... I can detect a very noticeable difference.
Both Performance and fuel mileage suffer.
My fuel mileage will drop about 10 to 12 percent when using regular vs Premium.
Performance also takes a VERY noticeable hit.
 
#14 ·
I use 87. Always have always will. I used 93 in my Seville several years back for three tankfuls to see what the difference was. If I remember correctly I do believe that 93 octane, and a light right foot, netted me 1/2 mpg increase. So back to 87 for me. Anyway, this morning the wife and I were driving to go to breakfast, and a telling symptom happened. At a stop light, with the car misfiring which the wife felt, two messages came up. Service stability system and traction control. This same thing happened to me when I had a cracked spark plug. So now, since I changed out all of the plugs yesterday, I am thinking I have a bad coil. The same coil that was with the cracked plug (number 4) looked quite rusty. So I ordered an AC Delco coil while eating breakfast and when it gets here I will start with number 4. If that doesn't fix the issue I will change out the coils one by one until I find which one )if any of them) is the bad one. I also ordered a new MAP sensor last night so when that gets here I will change that out too. But I do believe that iy is going to be a coil

Don

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I use 87. Always have always will. I used 93 in my Seville several years back for three tankfuls to see what the difference was. If I remember correctly I do believe that 93 octane, and a light right foot, netted me 1/2 mpg increase. So back to 87 for me. Anyway, this morning the wife and I were driving to go to breakfast, and a telling symptom happened. At a stop light, with the car misfiring which the wife felt, two messages came up. Service stability system and traction control. This same thing happened to me when I had a cracked spark plug. So now, since I changed out all of the plugs yesterday, I am thinking I have a bad coil. The same coil that was with the cracked plug (number 4) looked quite rusty. So I ordered an AC Delco coil while eating breakfast and when it gets here I will start with number 4. If that doesn't fix the issue I will change out the coils one by one until I find which one (if any of them) is the bad one. I also ordered a new MAP sensor last night so when that gets here I will change that out too. But I do believe that iy is going to be a coil

Don
 
#16 ·
Well the culprit for my issue may have been a bad tank of gas. But I will not know for sure until tomorrow morning. I get a call from my wife this afternoon telling me that my daughters car is broke down at college. I told her to call AAA and have it towed home I will look at it after work. So I get home and the car will run with throttle input but will not idle. I cleaned the throttle body and it wanted to run. So I cleaned it up pristine and put five gallons of fresh premium in it and it is running great now. By the way my daughter fuels up at the same station that I do. I also put a bottle of gas additive in both of our cars. I fueled up with a fresh tank of premium. So hopefully all is well now. And since I already bought the replacement coil I will be changing out the rusty one just for piece of mind.

Don
 
#17 ·
Well bad diagnosis on the bad gas. It is still doing what it is doing. But a new MAP sensor arrived today and I installed it. Just idling in the driveway it feels okay. But I will find out on the drive to work tomorrow if it remedied the issue. I will update tomorrow

Don
 
#18 ·
MAP sensor did not fix the issue. Neither did changing out the rusty coil. So now I am going to remove the intake manifold again. I am going to replace the plenum, which does seem okay, and the intake gaskets. While the intake is off I will be giving the throttle body a hospital cleaning. There is also a wire harness that runs under the intake that the wire loom is all destroyed. I will be inspecting the wires closely, repairing if needed, and relooming the harness. Hopefully one of these will repair this issue

Don
 
#21 ·
I have a code reader but if the CEL isn't illuminated nothing will come up. I know that the Tech 2 can diagnose the sensors by checking their operation. But I am trying to avoid the $115 per hour charge my local dealer charges. But if it ends up being the TPS I think I have to go to the dealer. Not sure if the adjustment is a DIY thing. Can anyone tell me if it is doable?

Don

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Just checked my DVD service manual and it seems that there isn't a TPS. Instead there is a TPPS (throttle pedal position sensor). Is this accurate? I think the entire throttle pedal gets changed when replacing it. There is a relearn procedure for this that doesn't require a scan tool

Don
 
#22 ·
I have a code reader but if the CEL isn't illuminated nothing will come up. I know that the Tech 2 can diagnose the sensors by checking their operation. But I am trying to avoid the $115 per hour charge my local dealer charges. But if it ends up being the TPS I think I have to go to the dealer. Not sure if the adjustment is a DIY thing. Can anyone tell me if it is doable?

Don

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Just checked my DVD service manual and it seems that there isn't a TPS. Instead there is a TPPS (throttle pedal position sensor). Is this accurate? I think the entire throttle pedal gets changed when replacing it. There is a relearn procedure for this that doesn't require a scan tool

Don
Don... That is correct.
There are two potentiometers/rheostats, that have to match when you move the accelerator pedal.
Typically if either one of them mess up, the car will go into a Fail Safe / Reduced Power mode and you can't drive over about 15 mph.
 
#23 ·
hey i got the same issue with my 07 some where just a mark or so from the cold to normal temp mine acts up while coasting to a stop engine surges amost to 500 rpms then stalls or redeems it self changed gaskets ,,,plenum,throttle body gasket ,temp switch no luck either good luck we might have to resort to man
 
#25 ·
Don

Have you check the IAC counts ,throttle angle and MAP voltage and compared them Hot and cold.
Can you post them or PM me. You may have other problems.

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I know my scanner has live data but not sure to what extent. I will see what I can come up with and let you know. One thing I discovered is when I floor the accelerator it has a big gulp sound and then revs up. Seems a bit strange. I am still thinking I have a vacuum issue. But I will be the first to say that since cars became technical I am not very good at diagnosis

Don
 
#26 ·
So I hooked up my scanner and all of what you were looking for aren't options. TPS gives me a % mot an angle. At idle the % is 18.0 + or - 0.5. What did catch my attention was the ignition advance. This may be normal but doesn't seem right to me. At idle it is darting around at a rapid rate. High and low seem to be from 19 to 4. When I give it any throttle at all it goes up to 35.0 and higher. It is also very difficult to give this car minimal throttle. Idle speed is around 750. Trying to raise the RPM to 900 or 1,000 is nearly impossible. Even the slightest throttle brings the RPM up to 1,200 or so. Oh not sure that I mentioned this but as soon as the RPM is raised my issue goes away completely. I am still thinking I have a vacuum leak somewhere but if you have a different idea please let me know

Don
 
#27 ·
I'm having the same issues, see my thread p0300, I'm a mechanic and it has me stumped. sure feels electrical in nature, comes and goes, runs ok on highway, warmed up at idle starts chugging and flagging various lights. stuck valves seems odd, I run good gas and did fuel flush, made no diff. going to pull off intake and check for carbon build up, probably change crank sensor while in there. I know suppose to resync cam and crank sensors, also read about ecm reflash to address various issues. I think sticking valves were more problems on older nstar
 
#28 ·
At least you get a code. I wish I would get a code to at least point me in a direction. I do not believe I am having valves sticking.

Don

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At least you get a code. I wish I would get a code to at least point me in a direction. I do not believe I am having valves sticking.

Don

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Okay I have a question. There is a wiring harness that runs under the intake manifold that I think is for the knock sensors and cam sensor. The wire loom is disintegrated on the harness. Just wondering if this can be related. Would a faulty cam sensor or knock sensor cause the issue I am having? Knowing the loom is gone it may not be a bad sensor but bad wire.

Don
 
#30 ·
Well this morning I decided that when I remove the intake manifold I am replacing everything under there. So my plan is this.

Replace plenum boot and intake manifold gaskets
Replace crankshaft position sensor
Replace knock sensors
Replace wiring harness that feeds CPS, CKPS, Knock sensors
Remove and clean EGR valve
When intake is off clean throttle body to "lick it" clean

Hopefully one of these will repair the issue. All totaled there is about $240 in parts. Is there anything else that I should do while the intake is off? I do not want to have to remove the intake manifold again so I am trying to cover everything.

Don
 
#32 ·
I don't want to sound unappreciative but am I the only person who has read about multiple paid dealer visits due to misdiagnosis and replacing good parts out. I will not consider having a mechanic touch my car until I have done the work listed. Even then I may search more.

Don
 
#34 ·
I figure that at the dealers $115 per hour labor rate I can change out a lot of parts and still be cheaper than what they would charge me to replace the knock sensors and the crank sensor. that job would be three hours minimum. One hour for diagnosis and at least two hours for repairs. So that job alone would run me $500 minimum including parts. I am far less than that into this so far.

Oh I removed and cleaned the EGR this morning. EGR looked fine and no change with the cleaning. Once the harness arrives (should be by Tuesday) I will do all the other work.

Don
 
#36 ·
I think I am covering the bases for vacuum leaks with the intake overhaul. Aside form the intake the only other vacuum line I see is the brake booster. There doesn't appear to be any of those emissions tubes anywhere. The wiring harness arrived today so I am going to do this job tomorrow morning. Fingers crossed

Don
 
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