Idles rough, hesitates and sometimes dies because RPM falls too low

Tiny
ALKALINE
  • 1994 CHEVROLET SILVERADO
  • 230,000 MILES

When I start the engine it idles fine to begin with. I put it in gear and start driving, and by the time I get to the end of the street it has been stalling. I start it again, and it idles low and rough. When I give it the gas it hesitates badly.

I have replaced the IACV, TPS, ignition coil, cap, and rotor. A couple of months ago I rebuilt the TBI (including new fuel pressure regulator). I removed the EGR valve to examine for carbon buildup in the manifold passages beneath it and they were clear. The EGR valve itself has been replaced within the past few years. The coolant temp sensor on top of the manifold next to the water inlet is also fairly new at around six months old.

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Wednesday, November 23rd, 2011 AT 12:33 AM

13 Replies

Tiny
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Is fuel pressure within spec? Have you checked for vacuum leaks? Any trouble codes?

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Wednesday, November 23rd, 2011 AT 12:36 AM
Tiny
ALKALINE
  • MEMBER

The CEL came on twice during the past dozen or so times that I've driven it. On both occasions, the light reset/turned off after I turned the truck off. It is my understanding that I can't retrieve the code if the CEL has gone out. Is that correct?

I have visually inspected all the vacuum lines and can find no leaks.

Fuel pressure is something I've never checked. How can I do this?

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Wednesday, November 23rd, 2011 AT 1:43 AM
Tiny
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If it is a hard code, it will stay in memory. If you can, give it a try to see if anything is showing. Also, if this happens when driving, you can use a live scanner to monitor the systems to see what is happening.

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Wednesday, November 23rd, 2011 AT 3:51 AM
Tiny
ALKALINE
  • MEMBER

OK, just checked the code. It gave me a 44.

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Wednesday, November 23rd, 2011 AT 4:33 AM
Tiny
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That is for a lean exhaust. Most likely a vacuum leak. Also, it could deal with the temp sensor or low fuel pressure.

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Wednesday, November 23rd, 2011 AT 4:45 AM
Tiny
ALKALINE
  • MEMBER

Just checked for vacuum leaks using some spray carb cleaner. Didn't find any leaks. I also just now replaced the fuel filter.

It is still running rough and almost died when I got to the end of the street like it has been, but it might be running just a tad bit better than it was. I can't really know for sure until later on today/tonight when the temperature outside drops. Cold temperatures exacerbate the problem.

Since it is worse when it is cold outside, does that favor the problem being a bad temperature sensor vs. A bad fuel pump?

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Wednesday, November 23rd, 2011 AT 7:25 PM
Tiny
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It could be either. Pumps can act funny in cold weather too.

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Wednesday, November 23rd, 2011 AT 8:25 PM
Tiny
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  • MEMBER

Will be replacing the fuel pump tomorrow. I'll update this thread with results.

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Friday, November 25th, 2011 AT 1:57 AM
Tiny
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Before replacing it, check the pressure it is producing. It's a lot of work and money if it isn't bad.

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Friday, November 25th, 2011 AT 4:20 AM
Tiny
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I think I may have found the problem. I think the temp sensor connector wasn't making good electrical contact. I removed the connector and applied some dilectric grease to the contacts. (I had replaced this sensor a few months ago and did not use any dilectric grease on it at that time). When I took it for a test drive around the block it ran fine. I'm soooo glad I looked at that before I dropped the tank and replaced the pump! I'm cautiously optimistic that this has fixed the problem. We shall see.

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Friday, November 25th, 2011 AT 5:16 AM
Tiny
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That is good news. I hope that fixes the problem. Removing the tank is a pain.

Happy Thanksgiving,

Joe

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Friday, November 25th, 2011 AT 5:26 AM
Tiny
ALKALINE
  • MEMBER

Update: Well, my temp sensor connector theory was apparently just wishful thinking. We had a cold front blow through and the truck was running really bad in the cold weather. Since my truck has TBI, I don't have a nice handy fuel rail with a Schrader valve on it to check the pressure from. I went to the parts store to price out a fuel pressure gauge and the gauge kit I'd need that has the inline adapter costs as much as the new pump itself. So I decided to skip the gauge and just install a new pump. It wasn't really that big a deal. Took me three hours start to finish. That was totally the problem! It runs like a new truck now! I wish I had started with replacing the fuel pump instead of throwing other parts at the problem.

Thanks for your suggestions! You pointed me in the right direction.

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Tuesday, November 29th, 2011 AT 11:10 PM
Tiny
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I'm glad you got it fixed. You sound like you have the same luck as I do. (Lol) I don't know where you live, but in my area, most parts stores will lend the gauge and adapter to customers with hopes to sell a new pump. Regardless, I'm glad you got it fixed.

Take care and let us know if you have questions in the future.
Joe

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Wednesday, November 30th, 2011 AT 1:12 AM

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