I'mma start by saying that this is my first time ever owning a TBI truck and so far I'm not having a good time with it. I've had both prior gen carbed small blocks and the 5.3 and later lq and ls based small blocks and both have been much more complacent and easy to fix.
Also, before making this thread I did a keyword search and read a few threads and didn't find anything like the issues I'm having.
So here we go.
Truck: 1995 C1500 Silverado W/ 5.7L TBI engine and 4L60e.
What's been done:
Bought the truck with a clogged cooling system running straight water and a blown head gasket.
- Took off both heads and had a valve job done on them and also inspected for cracks.
-used a fel-pro head gasket kit and used new head bolts that were tightened following instructions from a Haynes Repair manual.
-had the intake manifold pressure cleaned and sand blasted and the coolant and egr passages cleaned.
What's going on:
The truck refuses to idle where its supposed to.
Right now it's idling at +/- 1,000 rpm. Since idling high, the transmission has also been shifting much higher in the RPM range. Sometimes the RPM will also rise and drop a bit and then settle at 1k again.
One night, I started it and it was suddenly idling right and it drove and shifted flawlessly. Turned it off and back on and it went back to not idling or shifting right, so I think the late shifting and idling high are related.
I've spent HOURS on forums searching through threads looking for answers and almost always end up with people pointing at the IAC valve or the TBI base plate gasket.
Following the advice of one of these threads I removed the IAC valve and plugged the hole... The truck would not start. I unplugged the hole and let it start and as expected it idled super high. Then, while running I plugged the hole and it idled SUPER low, like at 450-500, which the thread said it was supposed to.
I've changed the IAC three times. Two times with a YCT unit and this last time with an ACdelco one. Still the truck idles at 1k rpm.
I've checked ignition timing with a timing light and its right on the money.
The TBI base plate gasket is brand new as it came with my gasket set.
Also the second time I changed the IAC valve with a YCT unit, the truck idled even higher at 1,500 rpm and I could hear a loud vacuum sound coming from inside the carb. That's why i ditched YCT and went with ACdelco, but still the truck wont idle right.
My Haynes repair manual has nothing on high idle, so I have no idea what else to do.
I've clamped down on the brake booster and crankcase ventilation hoses and it's had no effect on the idle speed. I've checked the vacuum hoses for cracks and haven't found any, but I doubt it's a vacuum leak because of that one night everything worked perfect. A vacuum leak wouldn't just go on and off with an ignition switch cycle.
Any help will be appreciated because I don't know what else to do.
Sent from my moto g(6) plus using Tapatalk
Also, before making this thread I did a keyword search and read a few threads and didn't find anything like the issues I'm having.
So here we go.
Truck: 1995 C1500 Silverado W/ 5.7L TBI engine and 4L60e.
What's been done:
Bought the truck with a clogged cooling system running straight water and a blown head gasket.
- Took off both heads and had a valve job done on them and also inspected for cracks.
-used a fel-pro head gasket kit and used new head bolts that were tightened following instructions from a Haynes Repair manual.
-had the intake manifold pressure cleaned and sand blasted and the coolant and egr passages cleaned.
What's going on:
The truck refuses to idle where its supposed to.
Right now it's idling at +/- 1,000 rpm. Since idling high, the transmission has also been shifting much higher in the RPM range. Sometimes the RPM will also rise and drop a bit and then settle at 1k again.
One night, I started it and it was suddenly idling right and it drove and shifted flawlessly. Turned it off and back on and it went back to not idling or shifting right, so I think the late shifting and idling high are related.
I've spent HOURS on forums searching through threads looking for answers and almost always end up with people pointing at the IAC valve or the TBI base plate gasket.
Following the advice of one of these threads I removed the IAC valve and plugged the hole... The truck would not start. I unplugged the hole and let it start and as expected it idled super high. Then, while running I plugged the hole and it idled SUPER low, like at 450-500, which the thread said it was supposed to.
I've changed the IAC three times. Two times with a YCT unit and this last time with an ACdelco one. Still the truck idles at 1k rpm.
I've checked ignition timing with a timing light and its right on the money.
The TBI base plate gasket is brand new as it came with my gasket set.
Also the second time I changed the IAC valve with a YCT unit, the truck idled even higher at 1,500 rpm and I could hear a loud vacuum sound coming from inside the carb. That's why i ditched YCT and went with ACdelco, but still the truck wont idle right.
My Haynes repair manual has nothing on high idle, so I have no idea what else to do.
I've clamped down on the brake booster and crankcase ventilation hoses and it's had no effect on the idle speed. I've checked the vacuum hoses for cracks and haven't found any, but I doubt it's a vacuum leak because of that one night everything worked perfect. A vacuum leak wouldn't just go on and off with an ignition switch cycle.
Any help will be appreciated because I don't know what else to do.
Sent from my moto g(6) plus using Tapatalk
