1999 3.8 GS engine surging

Recently my 91k 1999 Regal GS has started to engine surge (cycles up / down 400-500RPM) but only during light engine loads.

-It happens in cruise going up a slight incline on the freeway.
-When lightly accelerating up an on ramp.
-Seems to coincide when boost pressure comes on.
-Happens with or without cruise control turned on.

Otherwise the engine idles fine, does not miss, does not surge at lower speeds and runs smooth at heavier loads.


For what its worth, a month ago I changed out the battery (engine was without any juice for 24 hours - can the computer lose factory settings if left for this long???). I also switched to running on 87 Octane 100 % gas (no ethanol blend at the pump) for the past 4 months (no pinging and mpg were up to 34 on the freeway). Since the engine surging, I've switched back to 93 Octane and the problem is still there......

Ideas????

You are getting some minor "chuggle" or "fishbite" which is the torque convertor locking/unlocking.

Disconnect the negative cable to the battery and let it sit overnight disconnected. Reconnect and then see what it does.

In a worse case you may need the PCM reset to force it into relearn mode and clear the adaptive shift points.

After this original post, I took the car into the dealer. They diagnosed carbon tracking - leading to new plugs and leads. I guess it was time for a new set, but it still didn't fix the problem.

I will try the battery trick tonight.

I was thinking that the computer had lost some adaptive settings after the battery change and didn't learn correctly after I put the new battery in. From what you say, I should try another reset (I guess you imply that leaving power off does this and and since I don't have a handheld that will have to do)

I also came across another post.....
http://www.carcomplaints.com/Buick/Regal/1999/tsbs.shtml
specifically-

VEHICLE SPEED CONTROL
TSB #050604058 -- INTERMITTENT CHUGGLE OR FISHBITE ON LIGHT ACCELERATION OR A HIGHWAY SPEEDS WITH NO DIAGNOSTIC TROUBLE CODES (DTCS). *TT (NHTSA ID #10017568, SEPTEMBER 01 2005)

Two things additional posts recommed are the TBS and the MAF sensor. I'll try testing the TBS with a voltmeter tomorrow if the battery disconnect doesn't fix it (should be a linear 0.4V to 4V output right???).




Cheers....

Yeah I've seen the GM TSB that mentions the TPS as possibility. The voltages are about right. The only problem is I stopped recommending to anyone to replace it because it never fixes the problem but you never know.

Technically, when you remove battery power it isn't supposed to do anything in the form of PCM reset. But I know of a few instances where it worked so it is worth trying.

MAF is possible. To quickly illiminate it just disconnect the electrical connector to it and then take it out for a test drive. The PCM will use the programmed MAF/VAF tables without a signal from the mass airflow sensor.

Good luck!

How'd your situation turn out? I'm having a similar situation with a '00 MC SS.

How'd your situation turn out? I'm having a similar situation with a '00 MC SS.

What is your problem in detail? Maybe we can help.

What is your problem in detail? Maybe we can help.

I have the thread http://www.automotiveforums.com/vbulletin/showthread.php?p=4331345#post4331345 over in the Monte Carlo forum. I thought it may have been a light misfire that was occurring; but I guess it is a fishbite/chuggle that is occurring.

I have the thread http://www.automotiveforums.com/vbulletin/showthread.php?p=4331345#post4331345 over in the Monte Carlo forum. I thought it may have been a light misfire that was occurring; but I guess it is a fishbite/chuggle that is occurring.

Yes I saw that at Monte Carlo. I have documented 6 cases on AF where removing the battery negative cable overnight has supposedly cured their fishbite/chuggle problem. Give it a try if you have not already done that. Its free. Good luck.

Thanks to this forum, I just saved $1800. My 1998 Regal GS exhibited the "chuggle" described in this thread with the lockup engaging/disengaging. It first happened after the car sat for two weeks about a year ago. It eventually went away and we attributed it to gas that had turned bad. Once again, after sitting for two weeks last October, the same thing happened. It seemed to go away for a few months, then came back and was getting worse and worse. After my mechanic and a technician from the transmission company he uses test drove the car, the latter fellow determined it was a leaking valve in the transmission that controls the lock up. It would cost about $1800 to install a rebuild kit, including replacement of the valve. After reading this thread, I disconnected the negative battery cable overnight and "voila!" problem solved! We've driven the car four days and (fingers crossed), NO CHUGGLE!