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'88 TBI won't idle when warm

J

jann

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My '88 K5 TBI 350 seems to have developed a problem -- once it warms up, it won't idle. When the engine is cold it idles fine, then when it gets hot, the engine will die if I take my foot off the gas. I replaces my idle air control valve but that didn't help at all. It was running fine until about a month ago. Any suggestions what I might check?

Thanks!
 
its something electrical, what exactly is hard to say. could be the injectors, coil, ignition control module......
 
coolant temp sensor, O2 sensor, EGR valve or EGR valve actuator stuck open, vacuum leaks...
 
thought i already posted this..... but meh....

first step, scan for codes
second step, replace fuel filter, air filter and put a good injector cleaner in the tank
third step, check for excessive carbon buildup in the intake that could be effecting performance and indicates carbon buildup in cylinders and ports. if present, do a fuel induction service to clean it out.
fourth step, begin painful and time consuming diagnostic work of electronic engine controls and sensors.

proceed through steps until problem is resolved.
 
Ok I did some testing this weekend - here's what I found:

- no error codes from the ecu
- I found the IAC bypass procedure on this board and tried it with the engine warm - idle was TERRIBLE. Wouldn't even run unless i put my foot on the gas.
- fuel filter and air filter are good. Cleaned the TBI unit with carb cleaner.
- hooked up my ALDL cable and did some test runs. I'm running vortec heads and intake on the stock 350 bottom end but am still running the stock ECU program -- my BLM values are all over the place so I think it needs a custom tune...
 
Is there an idle air passage in the TBI unit that I should clean (in addition to the IAC fitting)?
 
It wouldn't hurt to take the TBI off and clean out all the passages on the bottom, including the PCV port in the front.

I'm gonna assume you've already checked for vacuum leaks and plugged the vacuum source for the EGR (if you have one) to eliminate that as a suspect...
 
The Vortec intake has an external egr connection to the exhaust which I haven't plumbed yet so I've just plugged the EGR port for now.

I sprayed the TBI passages out with carb cleaner and that didn't seem to change anything.

The timing is set to 0 right now - I'm gonna bump it a degree or 2 tonight and see if that helps the idle.

I'm determined to make it to the lake this weekend even if I have to drive two-footed :)
 
Check your coolant temp sensor. If it is reading cold when your engine is warmed up. The AF ratio will be too rich to idle good when warm.
 
x2 on the coolant temp sensor. You'll be amazed at how picky these TBI engines are about that little sucker.
 
i had a similar problem with a 1988 350 TBI... and it ended up being my EGR valve... it was actually seperated into 2 pieces but the stem was still in tacked.. so it would run good when i was on the throttle.. and would idle like i had a HUGE LOPY cam and wouldnt stay running... never through a code either...
 
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