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Engine is searching on cold crank up...


clockmaker's Avatar
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08-31-03, 05:52 PM   #1  
Engine is searching on cold crank up...

I replaced my o2 sensor and on cold crank up the engine seems to be searching for the proper idle speed . Do I need to replace my throttle position sensor. I have a 1993, 350, 1500ck with 94k miles on it. The engine burns no oil and seems to be getting better gas mileage with the new o2 sensor. Or what does anyone think I should do to fix the problem. Thanks in advance George K. in Alabama.

 
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09-01-03, 01:47 AM   #2  
If the engine smooths out after it warms up, I'd be looking more towards the coolant temp sensor..(not the sending unit for the guage). While you at it, what's the condition of the coolant? If it's nasty enough, it can effect the sensor, which could effect the cold start...

 
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09-01-03, 04:37 AM   #3  
The coolant is new, changed it 1000 miles or so ago and is mixed correctly. Could the sensor be bad itself? gk

 
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09-01-03, 05:36 AM   #4  
Joe_F
Check your throttle body gasket for problems. Spray some carburetor cleaner (not too much) at the base of the throttle body. If the idle changes, you have a vacuum leak. Pitch the gasket for a new one and tighten the TB to spec. Common problem.

Also, make sure your idle air control valve is working properly and the passage isn't dirty. Use autolibrary.org below to guide you.

 
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09-01-03, 12:19 PM   #5  
mike from nj
hopefully you used an a/c delco sensor---there are small differences and some vehicles just don't like non-original sensors.

did you unplug the battery, to reset the computer's 'learned' adaptive values--a lazy sensor will cause those values to go high(or low) and a new sensor will have a learning period for the computer until the adaptives come back to normal.

if you found nothing else so far from the other's above replies, you might want to investigate into intake valve deposits, they soak up fuel on a cold start, causing a lean 'hunting' idle, which usually smoothes out in a minute or two, (my car is horrendous for this) i don't know of any quick fixes for this, maybe a 'combustion chamber cleaner' spray can, let it soak for a good while, i've used this for C. C. deposits before with success. maybe even a good detergent brand of fuel might help. the only real fix is to physically clean the valves(that's why i live with it)

is there any smoke from the tailpipe when the idle is not smooth--clear can mean a lean condition, however black smoke can only be a rich condition, maybe a slightly leaking fuel injector?

let us know what you find

 
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09-02-03, 04:07 PM   #6  
Joe-F,
Throttle body gasket ok, did the spray check.

Mike from NJ,
Went by the chevy dealer, he said, Bosch was as good or better than A/C Delco, but he would sell me one If I needed it and.......If I unplugged the battery the truck may not learn what I want it to and it may also forget what it has learned so far and won't learn again and I would be in a fix. ( I do have the service manuals for this model truck in my house) so with that being said, what else could I do from my stand point. There is no smoke from the tail pipes and the pipes are clean inside matter a fact they may have some rust in them. When the engine is at operating temp it idles as smooth as a new one with no jerks or miss.
I will look into Joes air control valve issue tonight.

I appericate all of your help, George

 
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