Tahoe won't stop stumbling

[gradymotorco]

Hey everybody,

I have a 95 Tahoe with a Throttle Body Injected 350 V8 (Not the Vortec). It has about 175k on it, and for the last 6-7k miles I've been trying to get rid of this annoying hesitation/stumble/surging that occurs at above 50 mph. I've replaced the plugs, wires, fuel filter, air filter, pcv valve, cap, rotor, fuel pump, both injectors, and rebuilt the throttle body, and it still does it. I love my truck, but this is really aggravating and none of the shops I go to ever have much to say other than it's a 15 year old truck & its not going to run like new. Any suggestions would be really appreciated.

Thanks!

 

[gradymotorco]

p.s also replaced the trans fluid & filter

 

[Smoky14]

EGR

 

[gradymotorco]

if that's the case, should i just take it off & clean it or replace it?

 

[mechtech2]

EGR problems are my first guess, also.
Could also be ignition advance -not enough].
Is there crud on the back of the intake valves? This causes anomalies.
How about the cat or exhaust?

 

[beechcraftted]

My '95 Tahoe did this also.

My local shop removed the distributor and found the distributor gear worn to near failure. They wanted to replace the camshaft as well, but I cheaped out and just replaced the distributor gear. Still runs perfect to this day.

Something about the worn gear placing the static timing out of a range that the computer could not compensate for. I'm told this is a known problem from Corvettes from this era.

 

[willix]

EGR- if it has a distributor check the cap inside for tracks & corrosion . Some of those GM caps were pretty lame in the 90's

 

[98dakarM3]

Does the stumbling happen under load only? Such as when traveling up a hill or passing?

This stumbling can be an indication of a plenum/intake manifold gasket leak. Do you notice any coolant consumption?

 

[gradymotorco]

Thanks for all the prompt replies. As far as stumbling under load, it does, but it also does it when not under load & with the cruise control on, if that means anything. All I'm sure of about the exhaust is that it's completely stock, so a clogged cat is def a possibility. The truck has never had the Service Engine light to come on, but with it being OBD-I, I'm not sure if that really means a whole lot.

Thanks

 

[EvanD]

I have an 03 silverado which did same thing. I cleaned off the MAF with the cleaner spray and an intake cleaning. Fixed it.

 

[artificialist]

Originally Posted By: evandostert
I have an 03 silverado which did same thing. I cleaned off the MAF with the cleaner spray and an intake cleaning. Fixed it.

Unfortunately, TBI engines had a MAP sensor.

 

[SteveSRT8]

a clogged exhaust can be a vexing problem to diagnose.

Just disconnect the exhaust before the cats and take her for a spin.

 

[mechtech2]

Steve - Right.
I have had a few cars with cats with broken pieces.
They'd run great - sometimes. but if that piece bounced up randomly and plugged the pipe, the car s would run like poo.
Tough diagnosis!

 

[SteveSRT8]

yeah, my trickiest EVER was a 76 Dodge van, 318 auto. It would start and idle perfectly, even free rev, but get some load on it and it misfired and ran terrible!

Turned out the cat had blown out and the muffler was clogged.