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1991 Chevy Silverado Won't stay started when cold without f

Tiny
DEVINIA
  • MEMBER
  • 1991 CHEVROLET SILVERADO
  • V8
  • 4WD
  • AUTOMATIC
  • 210,000 MILES
I bought this truck a week or two ago and when you start it it will run if you keep on the gas but once it warms up to about 120 degrees it will stay idling fine but it takes a minute or two to get to that point. Any suggestions?
Thursday, July 22nd, 2010 AT 10:31 PM

13 Replies

Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 108,336 POSTS
It could be a few things. Do you know when the vehicle was last tuned up? Has the check engine light come on?
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Thursday, September 3rd, 2020 AT 9:38 AM
Tiny
DEVINIA
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Not sure on when it was last tuned and the check engine light is not on. I could change the spark plugs no problem but I didnt that could be the cause?
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Thursday, September 3rd, 2020 AT 9:38 AM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
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Honestly, I can't say that a tune up would fix the problem. However, there are many things that could cause this. For example, a sticking idle air control valve, EGR valve, temp sensor, throttle position sensor, vacuum leak. Just for the heck of it, remove one of the plugs and check its condition. That way we can eliminate that as a potential problem.
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Thursday, September 3rd, 2020 AT 9:38 AM
Tiny
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Well I did change the plugs and it seemed to get a little bit better. If one of those things you mentioned were the problem wouldn't that trip the service engine light? Which should I check/ replace first? Also the dash does read a temp.
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Thursday, September 3rd, 2020 AT 9:38 AM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
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I would start by removing the EGR and IAC and cleaning them and checking to make sure nothing is sticking. Without the check engine light, I don't like to recommend replacing anything. As far as the parts mentioned, they should set the check engine light, but sometimes they don't. Also, a vacuum leak many times will not set the check engine light.
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Thursday, September 3rd, 2020 AT 9:38 AM
Tiny
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Well I removed the IAC and EGR and cleaned them with Brake Cleaner and installed them and that didnt seem to make a difference, The EGR moves freely but I cant push in the IAC but im not sure if it is supposed to. I've searched for vacuum leaks and cant find anything. When I unplugged the temp sensor and it turned the check engine light on but the condition didnt seem like it changed much. Also nothing happened when the IAC was unplugged, no check engine light and the condition didnt change. Any advise will be very helpful.
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Thursday, September 3rd, 2020 AT 9:38 AM
Tiny
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  • MECHANIC
  • 108,336 POSTS
You should be able to move it. Go to a parts store and ask them to see one and compare it to yours.

Let me know what you find.
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Thursday, September 3rd, 2020 AT 9:38 AM
Tiny
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  • 16 POSTS
I went to the parts store and compared it. I could move the cylinder with the new one but it took some effort. A new one is about 60 bucks and I want to be sure before I spend that much on it but I was able to pick a used one that I could move the cylinder but with more effort than the new and the problem is still present. The resistance between the pins is 52 ohms on 1&2 and 3&4. When I twisted the IAC all the way out and started the motor it seemed to idle high and then I put my thumb over the hole and it went down and stayed steady.
Right when I start it it will die within 2 seconds pretty consistently unless my foot is in it?
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Thursday, September 3rd, 2020 AT 9:38 AM
Tiny
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Also, it will idle fine when the IAC is unplugged and most of the time wont die when it gets put in reverse or drive. And I took the IAC out and kept it plugged in and started the motor, it would move out but didnt look like it would move back in and that was the case with both IACs so I dont know if thats a problem or not.
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Thursday, September 3rd, 2020 AT 9:38 AM
Tiny
DEVINIA
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  • 16 POSTS
Did you give up?
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Thursday, September 3rd, 2020 AT 9:38 AM
Tiny
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ONever! I just got your email today. If both IAC do the same thing, I agree with you. I read back through everything we have discussed. Have you ever checked fuel pump pressure?
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Thursday, September 3rd, 2020 AT 9:38 AM
Tiny
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Glad to hear that you are still with me on this.
I havent ever checked fuel pressure before and I was curious to know how that could be the cause of the problem? Also I used propane to check for vacuum leaks and couldnt find anything. The motor from this truck was transplanted from a donor truck that had the same symptoms so thats why I dont think it is the fuel pressure unless somehow it was bad in both trucks?
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Thursday, September 3rd, 2020 AT 9:38 AM
Tiny
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That is interesting that they both had the same problem. I would still recommend checking fuel pump pressure to make sure there isn't a problem there. If you need directions, let me know.

Joe
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Thursday, September 3rd, 2020 AT 9:38 AM

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