Chevrolet Monte Carlo:

car stumbles with no acceleration in drive, but idles great

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# 1  7/23/2010 1:04 PM

New member
Registered: 7/23/2010
Posts: 2

car stumbles with no acceleration in drive, but idles great

2002 Monte Carlo LS 3.4  67 K Miles

Symptoms -  Car idles in park great,  but  instantly stumbles with lack of acceleration in drive.

It'll idle great... scan tool shows all sensors working although running lean,  but the instant I place into
drive and drive at 10 mph,  it loses all power, and will sit at 1500 rpm with NO acceleration,  then stumbles
and hesitates trying to move forward.  I can get it to accelerate by pulsing the gas pedal.

No codes are being set
A scanner  (Auto XRAY  DIY scanner) shows
Map is atmospheric  and drops to 12 inhg
MAF  is .61 lb/min  and goes to 9.45 lb/min in park with WOT before rpm limiter cuts in.
Timing is advancing  20 - 22
O2  Sensor  1 and 2  are ranging from .855  to low hundreds.
Engine Temp  changes as engine warms up.
Air Intake Temp sensor  changes as engines warms up
TPS  show throttle position  from 0  to 6%
ST  Fuel trims show a lean condition,  but trims are adjusted up and down

Tested  Fuel Pressure  50 psi  and goes slightly higher  when accelerated
Vacuum is about 40 inhg and steady.
plugs and wires have been replaced.  coil packs have been checked with an ohmmeter.  Ignition module was
tested 4 times.  EGR valve was replaced.  MAF  sensor was replaced.

I could not do a back pressure test as O2 sensor #1  was frozen in place and could
not be removed without damaging sensor and possibly bung.  So  a back pressure
test was not performed.  Not sure if there are other methods to  test for restrictive exhaust
beside removing the O2 sensor and using a back pressure gauge.

What do you suspect...   I'm kinda at wits end on this problem.   

Is there a transmission computer sending transaxle sensor signals  that my scanner is not picking up ??   
The auto Xray scanner seems very limited is there a better  DIY scanner which would show more signals
including  transmission error codes (if any)  ???

Could this be caused by a transmission sensor or transmission vacuum hose.

Restrictive exhaust ???  Not sure how to test without using a back pressure gauge,  but that
O2 sensor is not going to come out.  I've tried penetrating oil and a blow torch over several days
it is stuck in there real good  and as long as the O2 sensor is working...  perhaps there is another
method for eliminating a restrictive exhaust system.  Or possibly the symptoms are pointing to
something entirely different.

Not sure where to go from here,  but would appreciate this opportunity to learn more advanced troubleshooting

Thanks in advance for your recommendations and expertise...




# 2  7/23/2010 2:23 PM

Registered: 11/24/2009
Posts: 1301

Re: car stumbles with no acceleration in drive, but idles great

There is a special policy adjustment on the Catalytic Converter. It is Number 05551 (Sept 14, 2005).



Some customers of 2001-02 Chevrolet Impala, Monte Carlo; Pontiac Grand Prix; and Buick Regal model vehicles, equipped with a 3.4L (RPO LA1 - VIN E) or 3.8L (RPO L36 - VIN K) V6 engine, may experience a condition where the vehicle exhaust catalytic converter is replaced due to complaints of lack of power or illumination of the Malfunction Indicator Lamp (MIL).

This may be due to the front end cone insulation from the catalytic converter breaking away and blocking the front of the first catalyst brick and preventing the free flow of exhaust gas through the converter.

Special Policy Adjustment:

This special policy covers the condition described above for a period of 10 years or 120,000 miles (190,000 km), whichever occurs first, from the date the vehicle was originally placed in service, regardless of ownership. The repairs will be made at no charge to the customer.
For vehicles covered by Vehicle Service Contracts, all eligible claims with repair orders on or after September 15, 2005 are covered by this special policy and must be submitted using the labor operation codes provided with this bulletin. Claims with repair orders prior to September 15, 2005 must be submitted to the Service Contract provider.

Check with your local dealer to see if you still qualify for this policy.

You can get a copy of this in the service bulletin section of

One of the tests that were used when we needed to check a blocked exhaust without an O2 sensor to check backpressure would be using a vacuum gauge.

The information you sent me shows a vacuum reading of 40 in. This is a very high reading for this measurement. The normal reading for an engine is about 18 in of vacuum at a cursing speed. If the engine is running at 1500 RPM and has a reading of 40 in. and has no power then this is a sure sign of a problem and could be clogged exhaust or Catalytic Converter or intake problem.

If you can disconnect the exhaust from the manifold and run the engine you will probably see the engine run better and the vacuum drop to the normal number of about 18.

There are some scanners that will give you more information you are looking for, but they will cost you more. One scanner that I heard of that gives a lot of information is called Autel US703. You can find them at a good tool store or Ebay.

If this information doesn't help you, get back to us and we will look into this problem further.
car and truck information like nowhere else



# 3  7/23/2010 3:04 PM

New member
Registered: 7/23/2010
Posts: 2

Re: car stumbles with no acceleration in drive, but idles great

Thank you for your prompt and knowledgeable response.

I'm going to contact my local GM dealer and bring it in for service,  looks
like its covered under the TSB   2002  Monte Carlo  VIN Code E  3.4L engine
67000 miles.   Symptoms are solid.

Thanks for the hint for Autel US703.    Amazon carries it. The reviews were
positive about the performance of the unit but not very flattering concerning manufacturer support

Amazon did have some interesting debate about Equus vs Actron  so I'll look at all of the
above and make a choice.

Thanks again....  I'll get the car tested at the dealer and report back to you !!



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