Rough & low idle

Broken Rocker

Original poster
Member
Jan 8, 2016
8
McAllen
Hi guys, I have a 2002 Envoy 4.2 RWD.
I'm having this problem where the engine when it's warm, the gage indicates it's idling at 250 RPM, very very low, and feels like it's missfiring.
Now, some history for you...
About 6 months ago I changed the starter and used seafoam on the intake and gas only, not on the oil. Immediatly after that I took it for a test run after the seafoam, streched it's legs. Put it in 2nd, and gave it some pulls, after the 3rd one the engine died, and when I started it back it was running very rough and low (250rpm).
I ran it like that for 3 months until I discovered it was 3 coilpacks, changed them, and it's now running smooth again, but still idles @ 250.
I've changed those 3 coil packs, cam position sensor, VVT actuator, cleaned throttle body, 2 oil changes, new spark plugs. Nothing seems to get it.
BTW, I'm not getting any light on the dash.
 

xavierny25

Member
Mar 16, 2014
6,323
Staten Island, N.Y
Welcome to the nation :tiphat:

Just a thought but did you disconnect the battery or pull the fuses when you cleaned your throttle body? There a little procedure and a 30 minutes wait. That might clear things up for you.
 

Broken Rocker

Original poster
Member
Jan 8, 2016
8
McAllen
No, that wasn't done... what can that cause? There's no other issue, it performs well when I accelerate, and idles well when it's started cold. The issue starts when it's warm.

Welcome to the nation :tiphat:

Just a thought but did you disconnect the battery or pull the fuses when you cleaned your throttle body? There a little procedure and a 30 minutes wait. That might clear things up for you.

No, that wasn't done... what can that cause? There's no other issue, it performs well when I accelerate, and idles well when it's started cold. The issue starts when it's warm.

I've also gotten the oil pressure gage going flat dead but that's another issue I suppose, it got fixed when I changed the oil.
Also the dash message keeps saying that I should check the oil level, which is always fine.
 
Last edited by a moderator:

Wooluf1952

Member
Nov 20, 2011
2,663
Milwaukee, Wisconsin
The "flat dead" reading is probably from the low idle speed. Does the pressuer reading rise when you increase the idle speed?
Also, remember, the oil pressure reading on the 4.2 I6 is a lie. The sending unit is just an ON-OFF switch. Not a true pressure reading.
 

Broken Rocker

Original poster
Member
Jan 8, 2016
8
McAllen
The "flat dead" reading is probably from the low idle speed. Does the pressuer reading rise when you increase the idle speed?
Also, remember, the oil pressure reading on the 4.2 I6 is a lie. The sending unit is just an ON-OFF switch. Not a true pressure reading.

The flat dead oil pressure happened at idle and also at speed, cruising; but that's another issue caused by the oil pressure sensor.
 

Mooseman

Moderator
Dec 4, 2011
25,257
Ottawa, ON
It sounds like a flaky pressure sender/switch. It's a known failure prone part.
 

Forum Statistics

Threads
23,271
Posts
637,476
Members
18,472
Latest member
MissCrutcher

Members Online