Please Help with Rough Idle

[cshuman]

Smoke test the vacuum lines. Hell, smoke test everything. I had this problem with my bmw, one of my vacuum lines hidden under the intake manifold was torn in half, I know that this is a different engine, but I would check into it. You can also spray some starter fluid around and listen for the engine to rev up. Will confirm a vacuum leak. And then smoke test the area that you sprayed when the engine revved up. good luck man, hope you dont have to take it in. I die every time I have to take my cars in.

Edit: I re-read your post and I would be just about anything that you have a vacuum leak. The fact that you unplugged the maf and it smoothed out confirms. And the lean codes reinforce the diagnosis. Sorry if i'm repeating any advice. It's a vacuum leak. I'm a bmw guy and the 3 series are notorious for this and this is classic vacuum leak. Again I know this isn't a bmw engine, but this is a vacuum leak. Smoke test everything, vacuum lines around the intake manifold. Anything past the maf. check under the piping as well. They're pretty good at hiding. This is your problem. I'll buy you a beer if I'm wrong. Starter fluid, not propane, and smoke test, it's there, find a chart with all the vacuum lines, hit everything. Good luck man.

 

[chance942]

Do what I suggested with the dealers first buddy. It can't hurt and you'll save money.

 

[bpopp]

Just finished the plugs and wires. They looked fine and it didn't fix the rough idle. I agree re: the vacuum leak, but I just haven't been able to track it down using a propane bottle. How would one go about doing a smoke test? Is that something I can do myself or do I need to take it somewhere?

 

[cshuman]

Just finished the plugs and wires. They looked fine and it didn't fix the rough idle. I agree re: the vacuum leak, but I just haven't been able to track it down using a propane bottle. How would one go about doing a smoke test? Is that something I can do myself or do I need to take it somewhere?

Try using stater fluid, my experience with propane is that it disperses to quickly (because of the cooling fan moving air through there so quickly) so the leak never gets to pull enough propane in if any at all to hear the engine idle change. Starter fluid is a little easier to be precise with,doesn't disperses so quickly. I'll try and find a diy on the smoke test, I found mine before I needed to resort to the smoke test, so I can't honestly walk you through it.

 

[bpopp]

Found another hint that the vacuum leak diagnosis was correct. I noticed on Saturday that the air coming out of the vents would periodically stop blowing. I could still hear the fan running, and could feel cold air blowing on my feet, but the vents would go stagnant. After about 30 seconds, without me doing anything, the cold air would start blowing again as usual. I found another thread that talked about this issue and they said that a vacuum hose is used to open and close these ducts and that it defaults to closed. Gonna go over the hoses again tonight and see if I can find my leak. I wish I had a better vacuum diagram. The one in the service manuals and on the placard of my hood are not very good.

 

[alohamonte]

I've had a rough/low idle for months (I lost count).

I replaced the TPS, MAF, Plugs/Wires, Fuel/Air Filter, IAC, PCV, several EVAP do-dads and the idle was still terrible. Wanted to stall when warm. Lots of double-pedaling at stop lights.

I pulled the upper intake. Two of the three gaskets were leaking. The injectors were heavily soiled. The injectors are soaking now. I HOPE this is the silver bullet!

 

[bpopp]

Well, I finally found my vacuum leak. I bought some plugs at Autozone and just started plugging stuff off going into the intake plenum. I still don't know exactly where the leak is, but I know it's somewhere between the VMV and the intake. There are two hoses that plug into the bottom of the intake plenum coming from the VMV (located under the battery). Each one has a white, plastic clip on it. I suspect the O-rings in these hoses has just gotten dry and brittle and is leaking. I plugged these holes going into the intake and my truck is running great again. The idle is normal and so far no check-engine light. Tomorrow I'll see if I can find a replacement hose at the dealer.