I have a 91 Chevy tbi 350 Goodwrench engine and I have had an idle problem for 21 months. I have been everywhere and no one can figure it out. The last month they put in another engine just like the one I had because they thought I had a internal coolant leak. Nothing has worked. All ignition parts have been replace including the distributor. Fuel pressure is not showing any problems either. Dealer says all tbi engines have a quiver but mine is more like it is cutting out and the truck is shaking and running rough at idle. Pressure regulator was changed too. Everyone says my injectors look fine. When I drive the truck in 3rd gear it shudders and shakes like it is missing and has no power unless you get down on it and then it will kick down and go. Any other time it drive fine as long as you don't let it idle.

 

oil pressure is good? a co-worker of mine has an 89 chevy silverado... same motor. He was having oil pressure issues, or so he thought. Truck ran great, just the gauge would dip low when he took off. Come to find out, some how the gauge was reading backwards, bc when you stab it, its supposed to raise the oil pressure if everything is working right.

so, idk if you've replaced that gauge/sender unit but check that and see... bc the gauge might not be showing you anything, but you might still have an oil pressure problem.

 

The oil pressure is good. It does not do anything weird on the gauge.

 

Sounds like it could be one of your injectors. Check the connectors and wiring , especially around the throttle body and where they connect to the injectors . Also look at the spray pattern with a flash light or a timing light , if you have access to one. Check at different throttle openings , should have a nice fine spray ,and not dribbling drops of fuel. How about the TPS ? Hope this helps .
Ron

 

It looks like the injectors are spraying like they are suppose to. The tps sensor has been changed too. The throttle body assembly was replaced with a new one because one of the first mechanics messed it up. Fuel pressure regulator was replaced but it didn't help anything. I have been dealing with this one mechanic for a year and he is just scratching his head at this point.

 

Ok , make sure you have the right injectors in the throttle body.They are color coded for the lbs. per hour, I don't recall which is wich. If that isn't it than I am as lost as you are.
Ron

 

is your tps votage right at idle???? i THINK it is supposed to be at .65 volts or close to there....

 

one more thing , make sure your computer is not screwed up.
Ron

 

The tps has been changed twice with no effect. The voltage was right when it was checked about a year ago. Alot of stuff has not been rechecked because in this long period the mechanic has been digging deeper to find the problem. He tried a new computer and new chip with no change. He has swapped the tbi off of another truck running good to see if it would change anything which should rule out the items on the tbi. Nothing changed. It sounds like it is cutting off and then it come back. The idle keeps changing. It is very inconsistent on what it is going to do. It does it cold and hot and really messes up in drive with your foot on the pedal. Yes the brake booster has been changed too.

 

well since we're talking about basics... how about ground wires? motor grounds, main grounds off the battery.