can anyone help??????

bulldawg1081 · September 21, 2004

I just recently purchased a 1989 GMC shortbed with the 350 engine and a 5 speed manual tranny and the truck runs fine other than it idles too fast and smokes black so i asked my local parts monkey and he recommended the little air/fuel/idle sensor(i forgot the proper name for it) so i bought it and went home installed that sensor,changed the plugs (it had the bosch platinums and i went back with the AC Delco R45TS)and changed the oil but it still idles fast and im unsure on what to do,this is my first fuel injected engine so its all new to me...is there anything else for me to check out??? does this happen often on the 350 TBI's?any input would be very helpful and greatly appreciated...1 more question,are the shortbeds with the v8 with the 5 speed like mine hard to find???

357mag · September 21, 2004

Sounds like a vacuum leak somewhere. Check the Idle Air Control motor, on the throttle body. Also look for a loose/broken/missing vacuum line. I'd hazard a guess as to your truck is way less common than the jillion or so with auto trannys. I too have a 5 speed NV4500 in my truck , but it's got the 8 foot box.

Tim sends

citydriver · September 26, 2004

The TBI base gasket may have failed..It was a common problem...I've also seen the intake gaskets fail, but mostly on the pre-Vortec 4.3L's

1992z71 · September 29, 2004

check the 4 vacuum lines and the gasket. I don't know how automotively inclined you are but a can of carb cleaner with the straw on it. Take the air claener off and spray the lines and around the TB. If that dosent change the idle check to see of the throttle position sensor in hooked up as well as the IAC Idle air control valve. How many miles are on the truck. You might have an injector sticking or not spraying likt it is supposed to at idle. Let me know if any of this helps. Ben

bulldawg1081 · September 30, 2004

check the 4 vacuum lines and the gasket. I don't know how automotively inclined you are but a can of carb cleaner with the straw on it. Take the air claener off and spray the lines and around the TB. If that dosent change the idle check to see of the throttle position sensor in hooked up as well as the IAC Idle air control valve. How many miles are on the truck. You might have an injector sticking or not spraying likt it is supposed to at idle. Let me know if any of this helps. Ben

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the truck has well over 500,000 miles on it but in suprisingly enough good shape,ive replaced the gasket under the throttle body,checked for vacuum leaks with some carb cleaner and found nothing not sure if the injector is working properly though

1992z71 · October 1, 2004

check those injectors. you also might hook a scan tool up to it and see if the 02 sensor is in range. It will cause it to run rich. plus it is a cheap investment for good gas milage. Ben

GMCSierra04 · October 1, 2004

Thats a lot of mile to have on any vehicle! For the high idle, check the IAC (idle air control valve) and see if its missadjusted or stuck. There probably is some carbon build that is preventing it to close off. For chekcing if the electrical part the IAC is okay, one wire should be 5v (source voltage from ECU), you ground should have low resistance and the return voltage to the ECU could be anywhere from 0-almost 5 volts. A digital multi meter is a great tool to use for this, being OBD I and not having a manufacturers specific scanner, your data stream will be very limited.

With black smoke you obviously have a rich A/F ratio so look at possible places that will give you more fuel than air. Such as plugged air filter, leaky or stuck injector, high fuel psi and so on. As far as checking the injectors, just pop off the air cleaner assembly and after its been running just shut it off and watch the 2 injectors. You will be able to see if they are leaking or are able to hold residual fuel pressure or you can just hook up a fuel pressure gauge. For checking your O2 senor, its probably non-heated so you'll have 2 wires going to it, 5v source and a return volatge wire which should read anywhere from 100mV to 900mV. The ECU can only compensate for A/F changes up to about 20% so if you O2 was not functioning then you would probably get a SES light. Let me know what you find.