Ghost in the machine....please help

[paulie]

Not sure where to post this but I am desperate guys, please help. Could be electrical, drivetrain, electronics, I just don't know anymore. I am STUMPED, and consider myself a pretty good mechanic as former Baja 1000, SCCA and NHRA race mechanic.

Car: 2001 Camaro V6; 86k and change on the odo; AT; drive by wire.
Mild mods (relevant): Flowmaster American thunder cat back, SLP under car ram air; MSD coils and wires, K&N filter.

At appx 2000 RPM and cruising speed, if you SLIGHTLY increase throttle pedal pressure, the car kind of bucks or surges tach varies about 200 RPM. No issues at idle or WOT. Symptoms same in D, or OD. Brake tap does not appear to change symptoms, so I don't think TCC.

Symptoms worse under load, going up hill or AC on, but once you get past 2500, smooth as glass-no issues.

really does not affect driveability, but is such a nuisance you either don't want to drive it, or roll at 80 MPH to avoid the issue.

I have heard it referred to as "fishbite" or "chuggle" which sounds appropriate for the symptom. Pulled TSB about same issue and TPS replacement. Bought TPS and discovered there is not one on my car, it is incorporated in throttle body on drive by wire.

Question(s): does it sound like TPS? Anyone hear of procedure to service the drive by wire TB other than replacing the WHOLE thing and all of its components? Could the TAC pedal assembly ever go bad?

It sure seems like something electrical, like a contact point that may be burned or corroded at the position that the throttle and butterfly are showing 2k on the tach.

Any help GREATLY appreciated. If you like close to me, there may be beer involved....

[flamingchicken]

Re: Ghost in the machine....please help

So I have the same problem, I just recently had the tcc update performed. I know there was alot of friction material in the pan of my transmission and I'm thinking it could be a torque converter issue. Although the tps issue is making me wonder. Talk it out?

[timthescarred]

Re: Ghost in the machine....please help

Mine does the same thing, but varies by about 500 rpm. Would love to find the reason but have no clues

[Rob Bell]

Re: Ghost in the machine....please help

For all three of you, I would suggest taking the ICM off and getting it tested. I have had two cars (not F-Bodies) that had those same symptoms, and it was the ICM. Before you do that though, check the plugs and wires. I'd also get the coils tested while you have it apart.

When my ICM's went, it would cruise fine, but accelerating lightly from a stop or when going slow would have it bucking, the tach would be flicking down then up. If I gunned it, the tach would jump all over the place, from like 2K to 6K RPM. It would just go nuts. it usually did it when the car was warm. But sometimes it would act up cold. But the wierd behavior you describe, especially under load, makes me think that's your issue.

[paulie]

Re: Ghost in the machine....please help

I changed the coil packs to MSD because I thought that could be it; while in there did the MSD wire upgrade and plugs too. Also, thought maybe O2 sensor so changed both of those.

I am not sure if it did this before modding the intake and exhaust, it is just louder now so maybe it seems more pronounced.

Curious, did you other guys upgrade to duals on cat-back, or running stock exhaust? Do you both have the SLP under car intake also?

I was thinking on blocking off one tailpipe with plumber's test plug and going back to single outlet to see if computer doesn't like exhaust with less back pressure, and maybe putting block off plate under air filter to back to essentially stock airbox config.

Maybe we can come up with something if we put our heads to it.....I hope...it's just so annoying.

[Rob Bell]

Re: Ghost in the machine....please help

Well since you just replaced the coils, wires and plugs, it's probably not those. I would still have the ICM checked though. Your issue sounds ignition-related, and the symptoms (at least in my opinion) point to the ICM. It's easy to remove, and if it's not the culprit, then fine. I just wouldn't throw any money at parts until it's confirmed good or bad.

[cam98aro]

Re: Ghost in the machine....please help

just to save you some time, it has nothing to do with the exhaust.. i have seen hundreds of people here with all kinds of exhaust and nobody has complained about the problem.

i drive a 5 speed, but my car also does NOT like 2000 rpm, the whole car will shake like it does when you hit the gas in gear and the rpms are too low (not the fast vibrating, but the entire car shakes back and fourth from the drivetrain shaking)

[paulie]

Re: Ghost in the machine....please help

mine kind of feels like that....I even used to describe it as "lugging" only I have an auto trans, not a stick....then I learned the term "chuggle" or "fishbite". I'll have to pull the ICM and see if they can test it for me.

[timthescarred]

Re: Ghost in the machine....please help

Mine is bone stock with an auto 4l60e, at 81k miles. It takes heavy acceleration fine as can be, I had the ICM tested 1 yr ago when chasing a misfire that turned out to be a faulty FPR.

I have new NGK TR55's (5000 miles) plug wires are 1 yr old and in good shape.

Now it could probably use a good intake cleaning.

[paulie]

Re: Ghost in the machine....please help

did the FPR change help the "lugging" symptoms? Does yours have drive by wire? I am just wondering if due to use the reostat, or what ever is the active mechanism on the TAC could have a burned contact because it seems to happen coincidentally at the point that you would typically be at on freeway cruising.

I can't think of anything else....was all set to test the ICM, but from what I gather you tested yours and it was not bad?

[timthescarred]

Re: Ghost in the machine....please help

the "lugging" has mainly been since the FPR change, I don't recall it before then, but that was over a year ago.

I do have the DBW system, and it's also been over a year since I had the ICM tested so it is possible that it has gone bad since that time.

I had been leaning more towards Tranny shift problems until I learned of the T5 with the same issues.

That points me toward PCM or throttle, its losing something while driving, air spark or fuel.

Also the ICM is only passthrough once the car warms up, When in open loop mode (cold) the ICM controls spark, however once in closed loop mode(O2 sensors warmed fully) the PCM takes over spark control and passes it through the ICM

[GinsuGuy585]

Re: Ghost in the machine....please help

It's the ICM.

They can FAIL to pass through correctly. I had this intermittent problem, and solved it with an ICM.

DON'T trust the testing machine at autozone (or any retailer), mine passed all the tests, but was eventually proven faulty.
When the ICM is in the engine bay it gets a lot hotter, electronics on the edge of failure are prone to normal operation in reduced temperatures, so on the counter being tested at 70F it will work, engine bay 150+F it will act... funky.

[Rob Bell]

Re: Ghost in the machine....please help

Good point GinsuGuy. When mine was tested, it did show faulty at room temp. But I can see, if it works OK at room temp, hitting it with a heat gun while on the tester to see if it acts up. Not enough to cook it, but just to get it good and warm.

[paulie]

Re: Ghost in the machine....please help

Well, I found an AC-Delco ICM brand new at amazon for $ 150 delivered. The coils are the Jeg's Hot Spark coils (basically black MSDs). The wires are MSD fat reds and the plugs have only about 5k mi on them (don't remember the brand)

Changed the ICM between rain storms, and got the cuts on my hands from the back side of the cowl buttons to prove it...hell, why didn't GM just anchor the cowl piece with razor blades?

Mother F'er still does it! I am thinking maybe TCC? On the driveway the idle is smooth as glass. Holding throttle steady at 1500 rpm NO FLUCTUATION. Holding steady at 2000 rpm NO FLUCTUATION. 2200 and 2500 NO FLUCTUATION.

Engine normal op temp; trans still cold (5 miles) up 6% grade with AC on...NO FLUCTUATION. All warmed up and up mild incline -----it's baaaaaack!!!!

It seems that this symptom occurs when the auto trans has reached op temp-does not present itself in cold trans....

Any ideas???

[timthescarred]

Re: Ghost in the machine....please help

Time for thread from the dead, haven't looked into this much but for anyone who is still researching just found this TSB


#05-06-04-058: Intermittent Chuggle or Fishbite on Light Acceleration or at Highway Speeds with No Diagnostic Trouble Codes (DTCs) (Replace Throttle Position (TPS) Sensor) - (Sep 7, 2005)


Subject: Intermittent Chuggle or Fishbite on Light Acceleration or at Highway Speeds with No Diagnostic Trouble Codes (DTCs) (Replace Throttle Position (TPS) Sensor)


Models: 1995-1999 Buick Riviera

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1995-2001 Chevrolet Lumina

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