I have a 2000 Monte Carlo SS. Recently I have noticed that at or around 50mph with light throttle input the RPM's seem to surge between 1500 and 2500. When this starts to happen if you keep a steady throttle the surge continues. As soon as more throttle is applied the surge goes away and its business as usual. The car idles and runs fine other then this surge. I have been thinking it is a vacuum leak somewhere but have searched several times and found nothing. Has anyone else experienced this problem? Can anyone give me some insight as to how to fix this issue?

Thanks in advance
Squidward

 

we may be pretty close on the vaccum leak. what you can do is take brake cleaner, the flammable stuff and spray it around the vaccum harness and also around the intake mounting surface and if it smoothes out that is where your problem is. also check your pcv valve just pull it out and make sure the valve is sittibg in the pcv valve propperly and also give it a little shake and make sure it rattles around in there. you can try taking the oil fill cap off and see if that changes anything. ive seen where on the 3.8 after the upper plenum is serviced the pcv tube is not properly installed.

 

Sounds like a bad O2 sensor or EGR valve........

How's your mileage?

What are your thoughts Chevy_jj or FD.

 

it could be and egr or a o2 sensor like tvanwinklehome suggested those would more than likely set a code. i was also thinking about your mass air flow sensor. if you pull it out and inspect it you may find the smallest amout of crap on the little sensors, it will be on the side the air flows from. if there is dirt on the sensor and you can clean it, BUT you must be very very very very carefull with those sensors they are paper thin and will break so very eaisly. i usually take a q tip and put some brake cleaner on the end and lightly clean the sensors but i cannot tellyou how carefull you must be. that part will put a hole in your wallet.

 

Which brings out a good question that should have been touched on at the top somewhere. Have you had it checked out for any codes? Which leads to more less obvious possible solutions. If your not throwing codes and you still get hesitation I would have your CAT checked. It may be a long shot but still jumping around in my head for some reason. But then again, if the CAT were clogged you would have more higher throttle issues.


TVW

 

Thanks for the input everyone . To answer a few of the questions that was asked in the above posts. The car as 71000 miles (and some change). The check engine light has never come on so I don't think there will be any codes. I have a code scanner at home so I will try to pull it later and see if there is any. The car idles and runs like brand new. There seems to be no power loss associated with this. It only happens between 50 and 60mph when you just cruising and have your foot light on the petal. As soon as your give it more gas it goes away. If you pop the tranny into 3rd it doesn’t happen because the RPM's are higher. We changed out the PCV valve thinking that might be the issue but it didn’t solve out problem.

Thanks
Squidward

 

i overlooked where you said 50mph so i looked on the computer for some ideas and this is what i found.

4T65E TCC Chuggle - kw hesitation hot intermittent misfire miss shudder surge warm #PIP3180A - (Oct 19, 2004)
4T65E TCC Chuggle
.

The following diagnosis might be helpful if the vehicle exhibits the symptom described in the PI.

Condition/Concern:
Dealers may comment on a chuggle, surge, misfire condition on 99-01 WB CB and HB cars equipped with the 4T65E at highway speeds.

Recommendation/Instructions:
If this condition is encountered

Carefully inspect the main engine wiring harness where it is routed by the A/C accumulator (this may differ between different engines).
Commanding the TCC on with the Tech 2 should eliminate the chuggle surge concern.
The TCC brake switch should also be inspected to ensure that it is not cycling.
If commanding the TCC on with the Tech 2 does not eliminate the concern, then repairs should be focused on the internal leaks.
If commanding the TCC on with the Tech 2 does not eliminate the concern and TCC slip speed is 30 RPM or less engine performance issues should be addressed
If inspection of the wiring harness or commanding TCC on with Tech 2 and or the TCC brake switch do not reveal the concern then obtain a snapshot during the condition. Graph the TCC duty cycle and look for a saw tooth pattern. TCC duty cycle will range from about 40-80%.
If this pattern is observed then the PCS is possibly out of range causing this concern. The following steps should be performed in an effort to correct the TCC chuggle condition.
A. The PCS should be replaced.

B. While the PCS solenoid is removed the Torque Signal Valve (321) should be stroked to ensure that it is not sticking or binding in the bore and the PWM solenoid inspected for being damaged.

C. If the Torque Signal Valve (321) is sticking or bind then perform the following Valve Body Cleaning Procedure.

With valve body removed and on workbench, carefully push valve against spring pressure to check if valve will snap back to original position. Or for the valves seated in home position, use a small flat blade screwdriver and carefully pry the valve off its seat, quickly remove the screwdriver allowing the valve to return to seat. If valve does not snap back unencumbered then the valve will need to be removed from the valve body.
Once valve is removed, inspect for any scratching or scoring.
If any is found, then the fingernail test will need to be performed.
Using your fingernail to move over scratches to see if nail will try to catch on the scratch or score.
If so, then valve body will need to be replaced.
It has been found that in most cases that the scratches are not severe enough to catch your fingernail.
In this case the valve should be cleaned with some type of contact or brake cleaner.
The bore should also be cleaned. Clean with machined side down so debris may escape.
Blow off with shop air.
To verify free movement of the valve, dip into clean ATF and install valve back into the appropriate bore, the valve should move freely. If the valve moves freely, in most cases the valve body will function properly when reinstalled.
Reassemble and retest .
After the PCS has been replaced and if necessary the Valve Body has been cleaned or replaced in extreme circumstances then both battery cables should be removed overnight to reset the TCC adapts in the PCM. (Touching the battery cables together will not reset the Adapt Values).
Install the battery cables and test drive the vehicle to see if the TCC chuggle has been eliminated. Proceed to step 14 ONLY if the condition is still present.
If the concern is still present after having the battery cables disconnected overnight the PCM should then be replaced.

alot of it may sound greek but its talking about your pressure control solenoid which have been pretty dilinquint lately.

 

Thanks for the input i will have a go at that this weekend [8D]

 

Let me know what it ended up being. My car is doing the exact same thing. I can actually get it to surge at lower speeds as well be around 40 to 50 MPH with light accleration it does it everytime. Car runs great except for that.

 

My 2000 SS is also doing this.Mycar is all stock with 163,000 miles [:-]. Its not really a big deal, but its kind of annoying. No codes kicked out, no power loss (Ran a 16.08 at the track last weekend), and I too cannot find a vacuum leak. Keep us posted if you find the problem...


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