Car has 152K miles and has been very reliable. When I drive it at 45 mph and try to gently accelerate to 50-55 mph the engine surges back and forth about 200-300 rpm. The tranny is in OD and I think the TC is locked. It looks like the boost gauge also shows a bar or two, then disappears, then comes back while its surging. I just replaced the TPS and it still acts the same. I replaced the LIM a few months back but it did this before and after the gasket swap. Any help?

when was the last time you did a tune up?
spark plugs, wires, pcv, fuel filter, 02 sensor?
try a can of fuel injector cleaner also.

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2006 Grand Prix GT

If the convertor is locked then there is on?y two things thatwill cause this. It is going to be either the sparkplug wires being carbon tracked and/or the coil towers internaly arcing. With the engine running have someone power brake the car and you spray salt water on the spark plug wire and look for arcing. Do this at night so you can see the arc. If nothing is arcing then the towers need to be replaced. You cannot test the towers. I have run acrossed them both before.

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99 Gtp XP cam, Map intercooler, PRJ fuel rail, Pro magnum 1.6 rockers, Titanium retainer, Wizaird air box. 4 inch Intake pipe, SLP headers, Cat delete, Paceset 3inch Exhaust, GMPP front rear sway bars and rear trailing arms,
HID lights, zzp 3.4 10 PSI. 13.269 @ 106.939 mph.

I would first check to see if you have a misfire. I am with Stingvett1, the coils are not as bulletproof as many people state. On my car I have been through 3 occasions of misfiring that ended with changing a coil to cure the problem.

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04 GTT - Retired
Best ET 13.016
Best Trap 115.56 MPH

Vic,

How do you check to see if its a misfire?

To everyone else,

I have connected the code reader, and it comes up clean.

The sparkplug wires on it are 8mm off a junk SC Riv. Its a long story, but I damaged one of the OEM wires, then tried the ZZP 10mm wires. But they caused a "quadrajet"-ish bog when I punched it at highway speeds. Then one day I was walking thru a junkyard...

The car has twice had its injectors "cleaned". I now consider injector cleaning right up there with snake oil, the Easter bunny and honest politicians....

Coils have been replaced. Two from the dealer and one from ZZP. The connectors are clean.

I want to say it was tuned up at 100K; so that was 50K miles ago.

I can tell with my aeroforce gauge, but I imagine a good scanner would have a function to read misfires as well. Your car will throw a code if you have a lot of misfires on one cylinder, but it you may have enough misfires to cause a problem and not trip a code. I would also clean out you MAF as well. When dirty they can also cause all sorts of symptoms and problems.

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04 GTT - Retired
Best ET 13.016
Best Trap 115.56 MPH

Can I use carb spray to clean out the MAF?

They make a specific MAF cleaner you can pickup at the auto part store.

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04 GTT - Retired
Best ET 13.016
Best Trap 115.56 MPH

If you could call that surge a stumble on light accelaration at cruise. I would take a serious look at the EGR system. Carbon from the exhaust will gum things up. The PCM won't set a code until a problem exists for longer than 20 seconds. There used to be a lot of problems with the feedback sensor, but these are a newer design. Good luck.

your using used spark plug wires? I would suggest doing another tune up, is your car stock? if so, get new AC\Delco 41-101 plugs, and AC\Delco wires, use di-electric grease. What I've found with plug wires that have a lot of miles on them, once you take them off\touch them, they're no good anymore.

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2006 Grand Prix GT

I was thinking about getting a new set of plug wires. Maybe this is my reason to do that.

I also like the comment about the EGR. I'm assuming that I can just disconnect the vacuum supply (and plug the hose) to disable the EGR. I'm familiar with other cars but have not worked a bunch on this car.

on the 3800 just unplug the electrical connector for EGR

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2006 Grand Prix GT

Well I unplugged the EGR and it did the same thing. I did verify that the surging is only when the tranny is in OD and the TC is locked. I've read elsewhere that the TC solenoid go bad on these trannies. Could that be the souce of the "surging"? The TC locking/unlocking. Does anyone know how can I test the solenoid?

I doubt it's the solenoid, did you change the wires yet? With the TC locked in 4th, the engine is under very heavy load. If you have a scanner you can scan for misfires. The TCC Solenoid rarely fails, although the TCC apply valve could be worn, I doubt that is your problem.

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2006 Grand Prix GT

Well just put on a set of brand spanking new wires from the stealership. Good ol' AC Delco's. Same problem. The wires on the the car from the JY had "Packard" printed on them and were 8mm as well.

So what else should I look at?

try a seafoam treatment, pour one bottle in the gas tank, 1\3 in the oil, the rest in the vacuum line connected to the brake booster, goto our DIY section for instructions. What plugs are you running again>

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2006 Grand Prix GT

Stock plugs.

I've tried the injector cleaning route twice before with out any noticable changes to the car's performance.

coil pack?

I would suspect the TCC solenoid. They are a fairly high failure part, and the speed you indicate is where the TCC locks up, and the RPM variance is about right. Replace it, and the PCS solenoid while you're in there, since they fail commonly as well.

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One Big Ass Mistake America

I was thinking coil packs too. But is there a way to tell which of the three might be bad? Two were replaced around 125K miles and the third around 140K miles. The car has 153K miles right now. I saw some MSD ones at the parts store and they were going for $50 each . I've already replaced the TPS and the plug wires without solving the problem...

Is there a code reader for the TCC solenoid?

Does it do it when the tranny is locked in 3rd? To test coils measure resistance across the terminals. Check triple edge website, tcc solenoid rarely fails, and when I was working at the tranny shop, we never saw a 4t65e tcc solenoid fail

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2006 Grand Prix GT

Yes the "surging" is when the engine is warmed up, and the tranny is in OD and the TC is locked up. If I gently try to accelerate the engine "surges" about 200 rpm up and down as the vehicle slow increases in speed. If I "jump" into it or try to accelerate more aggresively the tranny drops a gear and engine takes right off.

Shit, those solenoids fail on a regular basis. Seen MANY 4T60, -65, & -80 solenoids fail. We stock a handful at our low volume dealer.

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One Big Ass Mistake America

Dang, I've seen the PCS fail all the time, usually with TCC it's the valve in the valve body that fails, we never had to replace a TCC solenoid, just the valve, or in some casses the valve body itself

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2006 Grand Prix GT

Well I might be onto something. I did a vacuum leak check with carb cleaner and found that the PCV cover and the vac fitting that supplies vac to the brake booster were leaking. I put a new gasket on the cover and bought a new vac distribution fitting that has the o-ring with it. I took it for a ride and the surging is barley noticable now. I might use WD-40 tomorrow and see what else is leaking.