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Ivan, ASE Certified Master Technician
Category: Chevy
Satisfied Customers: 4871
Experience:  ASE Master Tech. 20+ years experience. 9 years self employed. Expert on AUTOLAB Radio Show
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1995 Chevy: mi..350 TBI/auto Rough idle &..accelerate..carb

Customer Question

1995 Chevy K1500 203K mi. 350 TBI/auto Rough idle & hesitating
Everything was good until I stopped at a red light and the idle dropped really low and rough, when the light changed I tried to accelerate but had no power, stumbling and hesitating, felt like I was running out of gas but had almost 1/2 tank.It feels like an old carb with a bad accelerator pump, give it a little gas and it falls on it's face.
So far I have tried:
Pulling Codes (44 lean condition)
Fuel filter (this got it drive-able but still poor running)
Plugs, autolite 25
BG44K and drove it a bit.
Idle air control valve
EGR (it was bad but didn't change the way it runs)
Tested fuel pump 10 psi, no more no less.
I found a tbi gasket kit so I tore down the tbi to change the filters that are on the injectors, didn't see anything that looked too bad, even the injector filters didn't look too bad.(was hoping they were a little dirty)
The injectors seem to have a good spray pattern compared to what I've seen them like in the past.
I just took it out for a test drive and it still gave me code 44 and ran crappy, (it did seem like it got worse after it warmed up)
Less than a year ago I was having trouble passing my smog test and performed the following repairs.
Plugs, wires, cap and rotor.
Bosch O2 sensor
Cat Converter.
I cant find vacuum leaks.
Everything looks good under the hood.
The only thing I can think of is the injectors but they look like they're fine
Ever had the same problem?
Any ideas?
I'm stumped.
Submitted: 7 years ago.
Category: Chevy
Expert:  Ivan replied 7 years ago.

Hello and good afternoon. I'd like you to try something. Evidently we must have a fuel distribution problem, since you are getting a lean code paired with a power loss. I'd like you to get one of the blue propane bottles. Hook a vacuum line to it and attach it to a vacuum port so you can inject it into the intake or throttlebody. I'd like you to get to the point where you don't have power, then open the valve and see if the engine spunks up and responds to the propane. Let me know how it reacts.


Your JA Expert,


Customer: replied 7 years ago.

Great, my friend has my bottle!!

If the propane works what would I be looking for after that?


Expert:  Ivan replied 7 years ago.
Kevin, if the vehicle responds, we are going to focus on the possibility of either, bad fuel, restricted injectors, or possibly a coolant temperature sensor that is registering a very high temp. We also should focus on if one injector is stopping fuel flow.
Customer: replied 7 years ago.

Hi Ivan, Just an update, I havent gotten a chance to put the truck on the bottle yet but I have been checking for vacuum leaks and still cant find any, I was driving it on sunday and the check engine light came on, I pulled the codes and now I get a 35 and 44 (iac and lean). Odd the IAC was one of the first things that I tried, ( it was OE so what the heck!!)

I drove it again tonight and still had pretty much the same hesitation, the rough idle seems a little more intermitant than before and I was down to about 1/8 tank of gas so I gased up and i'm gonna drive it to work and see if the fresh gas helps any.

Any other ideas on the new 35 code?



Expert:  Ivan replied 7 years ago.

Kevin a vacuum leak is your most likely case. That would set both codes along with the hesitation. A lower intake manifold gasket is your most likely cause. Try checking fro the vacuum leak with carburetor cleaner around the perimeter of the intake especially on a cold start. If the idle changes at all, that will be confirmation.



Customer: replied 7 years ago.

Hi Ivan, thanks for the quick reply, I used about a half can of cleaner looking sunday and about a full can today and that was right after sarting it so it was cool, I sprayed it pretty good, all around the manifold and tbi, hoses, sensors, base of egr, whats so strange about it is, the problem came on so quickly, does that seem typical of an intake leak??

You know, I did notice that there was a small amount of steam (like when it's cold out) coming from the exhaust, but it seemed too warm today to have that, but it did rain heavy today about noon, but coolant passes through the intake (right?) hummmmmmm?????

What do ya think?

Expert:  Ivan replied 7 years ago.
You may have an intake leak between cylinders. That could cause a similar effect but not show to the outside. Very difficult to pinpoint. That IAC code really focuses on a situation where the computer wants a specific idle, but cannot achieve it with the desire IAC position.