Intermittent rough idle/loss of power

[Erinpl2131]

Hi I'm new to this forum. I recently purchased a 1999 yukon and almost immediately started experiencing while driving a loss of acceleration/power while trying to accelerate. My mechanic is at a loss. It is not the fuel pump, and he says all the codes are checking out fine. Weird thing is after I park it i come back to it and it drives fine. Last time I had it out, the problem seemed to get worse and worse until the truck died. Even trying to start it, it was rough and died. I had it towed to my mechanic where he said it fired back up and was acting completely normal. Fuel pump ok, no codes, no idea where to start. He said he would wait and see if he could catch it in the act and try and quickly diagnose it. I've been going there for awhile and they've been good to me. I was hoping to pool some experts and hopefully find an answer. At least find a direction. I've never had a mechanic say they are at a loss. Thanks ahead of time. Hope someone can help. Wanted to add a couple things. During the last episode, I heard what sounded like a backfire under vehicle as it tried to break 25mph. Also the fuel gauge flutters quite a bit. Not sure it has anything to do with it just thought I'd add.

---------- Post added at 11:39 PM ---------- Previous post was at 11:37 PM ----------

[/COLOR]One more thing I noticed the abs light. No idea why that came on during this issue.

 

[SunlitComet]

have a back pressure test of both exhaust banks done from start to the point at which it stalls. and did he actually verify fuel pressure the whole time from start to stall?

 

[Erinpl2131]

No, he hasn't witnessed it in the act. When it reached the shop they started it right up. If I understand what you're asking. Thanks for the response.

 

[crows feet]

i would say check timming or egr valve

 

[xanatost]

i would say check timming or egr valve

X2 on the timing. My buddie is having the same problem with his but the bolt that holds the distributer is his problem. See if you can turn yours and if so get it reset and tighten up the bolt. Also check to make sure the cap is not damaged and your plug wires as well.

 

[SunlitComet]

timing is controlled by pcm only. it can only be monitored in the vortecs. however if your dizzy was off a bit you would have been warned about it by means of the p1345 code.

 

[Erinpl2131]

So it's not the egr or timing?

 

[SunlitComet]

timing do not mysteriously lag off enough to kill your engine and magically repair it self after being shut down for a bit. so i would sugest just have it monitored by scanner and if no issues seen in the first few minutes move on. you can certainly monitor the egr data to with the right scanner but when you indicate the motor loses power till shutdown and wont restart right away but will later it sounds more like it can pump gases freely from getting clogged up or something electrical or electromechanical is having a possible thermal failure.

 

[retorq]

timing do not mysteriously lag off enough to kill your engine and magically repair it self after being shut down for a bit.

A failing ignition module, which plays a major role in timing, will most certainly do that. Intermittent issues when hot, when cool it's fine, eventually it will fail totally leaving you with no spark on the side of the road.

Your post is a fail post.

 

[SunlitComet]

on the vortecs the igniton coil driver acts as an electronic switch for the coil. all timing is handled within the pcm itself.