03-06-2010, 10:33 PM
Join Date: Mar 2010
1997 Bravada slight rough idle, runs great
Hey Guys - Need some assistance with a tough one.
165k, seems to have been taken care of. Original owners.
Recently had plugs and wires replaced as well as fuel pump. Filter was replaced too.
Came to me for rough idle and lack of power at times (lack of power that it can barely move). Also excessive fuel consumption?
Ok, so my first thoughts are clean the throttle, IAC and MAF - check. Throttle was filthy - didn't remove IAC when I cleaned.
Had 3 codes - 2 lean DTCs and a P0300. I didn't write them down cause the check engine light wasn't on when the truck came to me nor did the owner mention it being on.
My thoughts were that the lean DTCs were from the fuel pump going out along with the P0300 that may have set and the plugs/wires were replaced and nobody cleared the codes.
So I got it cleaned up but the idle seems a little rough in drive and reverse only. It idles nice in Park and N.
I drive the **** out of it, no problems, no lack of power, just the AWD shake these things are known for.
Well the engine wasn't getting hotter than 170 degrees, so I changed the t-stat now we got 200. Cool, there the fuel consumption.
No change in the idle.
I pull the EGR off and it looks fine and the pintle is seating all the way, but I clean it anyways. I verify the pintle holds with the carb cleaner in the valve and check for leaking at the pintle.
I sit down with the scan tool and start looking at stuff.
I see the IAC is being commanded to 0 and it's position is 0 as well. Also, the computer wants the truck to idle at 600 RPM but it won't go lower than 675RPM.
I command the EGR and it idles rough at 20% and 30% wants to die.
I command the Purge to 100% and the idle smooths out. I command to 0% and it runs like crap for a minute while it adjusts.
I check for vacuum leaks and find a few marginal hoses, replace them and the same thing.
It idles nice but I think it should idle smoother and better and the IAC should not be at 0.
When I put it in drive the desired idle is 550RPM but the engine still won't go lower than 650RPM.
As I ran it tonight, I think the fan clutch may be sticking. But that shouldn't cause this symptom but may also be contributing to the excessive fuel consumption.
Any ideas? It has CPFI but it runs great and doesn't seem to be the issue. It looks like a vacuum leak but I can't find anything.