Erratic idle/odd shifting only when cold! Please help!

[derekjl]

Just noticed this issue the other day on our ‘95 Tahoe, 350 TBI. The truck starts and runs fine otherwise, but after the RPMs come down to normal after a cold start, the truck will idle erratically UNTIL it is warmed up after about 10 minutes of driving. The tach will rhythmically jump maybe 150 rpms or so every few seconds when in park. The transmission also shifts at a higher RPM in each gear, especially 2nd and 3rd, again only until the truck is fully warm. This condition does not happen when in gear, only in park. Any help would be appreciated.


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[swathdiver]

Check for vacuum leaks and if you have another truck nearby I'd swap the MAP and or MAS (don't know if you have one of these) and see if they are going bad.

 

[bigfootchiro]

I was thinking potential vacuum leak too

 

[swathdiver]

I was thinking potential vacuum leak too

How's your repair coming along?

 

[bigfootchiro]

How's your repair coming along?

Still sitting dead in the water! Haven’t been able to get someone to help me take the trans out, since I don’t want to pay a shop to do it. My buddy has been sick lately, so he hasn’t been able to. I have the trans and transfer case, just have to drop it and put it in. Just don’t have the tools, nor experience to do it. The transmission isn’t my nemesis lol

 

[derekjl]

I was thinking potential vacuum leak too

Check for vacuum leaks and if you have another truck nearby I'd swap the MAP and or MAS (don't know if you have one of these) and see if they are going bad.

Just to reiterate, this issue is happening only for the first 10 minutes or so when the truck is coldest. It slowly goes away as it warms up. If it were a vacuum leak, wouldn't it be happening all the time, cold or warm?

 

[bigfootchiro]

Just to reiterate, this issue is happening only for the first 10 minutes or so when the truck is coldest. It slowly goes away as it warms up. If it were a vacuum leak, wouldn't it be happening all the time, cold or warm?

Not necessarily. As the engine warms up, heat causes components and gaskets to expand, which can make it seal tighter and close the potential leak.

 

[swathdiver]

There's some fellas on here that live not too far away, I'm sure they'd come over and lend a hand if you promised to feed them! I'd happily come by but am too weak to do that stuff at present.

 

[bigfootchiro]

There's some fellas on here that live not too far away, I'm sure they'd come over and lend a hand if you promised to feed them! I'd happily come by but am too weak to do that stuff at present.

I appreciate the offer! Where would I post up something like that looking for help? I can definitely supply food and beer lol. Why are you so weak right now?

 

[swathdiver]

Any of the forums I reckon. Diabetes complications.