Mechanics

CHEVROLET SILVERADO GAS PROBLEM

1991 Chevrolet Silverado • 225,000 miles

I have a 91 Chevy k1500 4x4 p/u with a idle issue. Truck starts and runs fine at first. Starts up, high idle comes on and than goes down. After driving for a while (approx 30 miles) when I shut off the truck and re-start it the idle is really fast. I have to fight the engine with the brakes to get it stopped. The idle never drops back down untill the engine has sat for a while and cooled off. When this happens the truck will go approx. 15 - 20 Mph and not slow down unless I use the brakes to stop
It. Also this weekend a new issue started where the brakes have no real pressure and I can push the pedal to the floor. Don't know if these are related or not? I've read so many diffrent things and don't want to just throw parts at it and get no where. Thanks, -Brandon
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Check your base of tbi unit for a blown gasket you can spray choke cleaner at the base and normally the rpm will change if it leaks. It probably is as this is one of the problems that crop up due to age. You'll just need to replace the gasket. Also check for soft hoses going to pcv and map sensor on firewall. Have your brakes checked and mkae sure master cyclinder is full of fluid it may be a master cylinder going bad or brake wear or both.

Hmac300
Dec 3, 2012.
If it was the gasket or the hoses wouldn't this be happening all the time? It only seems to happen after the truck is warm. Once cooled back down everything goes back to normal.

Not necessarily, heat expands things, also when engine is cold it's not in closed loop so it's running a little rich, whenit warms the computer can't make teh difference up to richen the fuel pmix enough to overcome the vacuum leak.

Hmac300
Dec 3, 2012.
Ok.I'll check those tonight. Thanks.

I tested the gasket with carb cleaner. It did not show sings of being blown, but I had already purchased the gasket so I went and changed the gasket anyways. It did make a significant difference. How ever I am still having a high rpm after I shut the truck off. Yesterday I drove home from work (aprox. 30 miles) and never had an issue. Parked the truck, went back out about 30 minutes later and the idle/rpm came back to being high/fast. Went into a store for about 15 minutes, started the truck and the idle/ rpms was back to normal. I checked the hoses and they appear to be ok. When I was working on the truck I removed the IACV to check what it looked like. The pintle had one shinny spot that was about a 1/4 of the pintle, shiny spot started from the top and tapered down. The rest of the pintle was black, almost looked like it wasn't seating flush inside the TBI when it was out? Any ideas on what I should check/do next? Thanks for all the help.

FYI I checked the breaks and found the pass side rear wheel cylinder leaking. Going to change the d/s and p/s cylinders this weekend.

Try cleaning iac then I fyou haven't already. But for it to reset you have to drive 40 mph for it to reset it self correctly. Only other thing I can think of is that iac is bad.
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Hmac300
Dec 6, 2012.
I cleaned the iac when it was out of the truck. I have driven already 120 miles so it should be set already? Have you ever heard of this before where it is only after the truck is shut off than turned back on that the problem is there?

No but stranger things h ave happened, I dorn' tknow what to suggest. Unless throttle is sticking due to age/mileage.

Hmac300
Dec 6, 2012.
I'm back. So today driving home the check engine light came on. Checked the codes. Got 22 (Tps- low signal voltage), 24 (vss- this I know about, the spedo has been out for some time, I have changed the vss and inst. Cluster, still not working, maybe a broken wire somewhere?) &Amp; 34 (Map sensor voltage low). Are all these parts somehow related? I really don't want to change the map and tps and find out the sensors really weren't bad. What do you think I should check?


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