Erratic Idle

grabber · 04-14-2009, 02:31 AM

My 7M idles terribly. When its cold it raises idle properly, but once warm jumps from 1000-2000 rpm's or so back and forth. I have checked the Throttle Position Sensor, the Idle Speed Control Valve and the Cold Start Injector in the way the FSM says and they all check out good... I'm lost and need to fix this, as the truck is close to ready to drive.

P.S. it is not pulling a check engine light, or any codes. Thanks for any help!

87mk111 · 04-14-2009, 02:35 PM

Have you checked your throttle linkage? That's the only other thing I can think of.

grabber · 04-14-2009, 11:11 PM

throttle linkage is smooth and free of any binding, etc... throttle does not move when the engine revs...

btwilson86 · 04-15-2009, 01:49 PM

Doe sit continuously rev up and down? If so, check your vacuum lines are not broken and are routed correctly. I had a couple switched around, took me forever to get rid of that revving...

grabber · 04-16-2009, 11:45 PM

I searched the engine for some bad vacuum lines... again... and found one that hangs off the rear of the intake thats plugged with a screw. Couldnt see anywhere to put it tho, and couldnt figure it out in the FSM, so could anyone take a look for me?

grabber · 05-05-2009, 11:58 PM

I checked out a couple other things with it today as well as eliminating all the emissions crap from the engine. When I unplugged the Cold Start Injector or the Idle speed control valve, the problem was still there, but when i unplugged the tps the engine revved up to around 3000 rpm and held there. Adjusting the idle screw did nothing. I think my next step will be replacing the tps, any ideas?

dunewarz · 05-06-2009, 06:07 AM

I would recommend checking the timing first. After 2 days of checking the tps and cleaning the iscv I found out that my timing was off causing the engine to run at high rpm. But I also found out that my iscv was dead so I manually adjusted it to the right position and so far no major problems, just a bit of bogging when you let off the gas and get back on it quick.

04-14-2009, 02:31 AM	#1
grabber Stock Join Date: Jun 2008 Location: waiparous Posts: 7	Erratic Idle My 7M idles terribly. When its cold it raises idle properly, but once warm jumps from 1000-2000 rpm's or so back and forth. I have checked the Throttle Position Sensor, the Idle Speed Control Valve and the Cold Start Injector in the way the FSM says and they all check out good... I'm lost and need to fix this, as the truck is close to ready to drive. P.S. it is not pulling a check engine light, or any codes. Thanks for any help!

04-14-2009, 02:35 PM	#2
87mk111 3" Exhaust Join Date: Mar 2009 Location: akron, ohio Posts: 226	Have you checked your throttle linkage? That's the only other thing I can think of. __________________ 87 N/A 5spd BHG, soon to be gte with r154

04-15-2009, 01:49 PM	#4
btwilson86 Super Moderator Join Date: May 2007 Location: Billings, Montana Posts: 1,034	Doe sit continuously rev up and down? If so, check your vacuum lines are not broken and are routed correctly. I had a couple switched around, took me forever to get rid of that revving... __________________ 1989 7MGTE R154 Targa Top White Package w/Blue Interior Driftmotion 57trim CT26, Upgraded Intercooler, 2.25" Hard Pipes, 3" Turbo Back Exhaust with Test Pipe, HKS VPC w/GM 3 bar MAP sensor, APEXi S-AFC, Walbro 255lph fuel pump, ProSport EVO Series Boost / Fuel Pressure / AFR gauges, Lotek a Pillar Gauge Pod, HKS Type 0 Turbo Timer, Eibach Lowering Springs, Tokico Illumina II TEMS struts, custom powder coated Motegi Racing TrakLite wheels

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04-14-2009, 11:11 PM	#3
grabber Stock Join Date: Jun 2008 Location: waiparous Posts: 7	throttle linkage is smooth and free of any binding, etc... throttle does not move when the engine revs...

04-16-2009, 11:45 PM	#5
grabber Stock Join Date: Jun 2008 Location: waiparous Posts: 7	I searched the engine for some bad vacuum lines... again... and found one that hangs off the rear of the intake thats plugged with a screw. Couldnt see anywhere to put it tho, and couldnt figure it out in the FSM, so could anyone take a look for me?

05-05-2009, 11:58 PM	#6
grabber Stock Join Date: Jun 2008 Location: waiparous Posts: 7	I checked out a couple other things with it today as well as eliminating all the emissions crap from the engine. When I unplugged the Cold Start Injector or the Idle speed control valve, the problem was still there, but when i unplugged the tps the engine revved up to around 3000 rpm and held there. Adjusting the idle screw did nothing. I think my next step will be replacing the tps, any ideas?

05-06-2009, 06:07 AM	#7
dunewarz 3" Exhaust Join Date: May 2009 Location: WhiteBear Posts: 54	I would recommend checking the timing first. After 2 days of checking the tps and cleaning the iscv I found out that my timing was off causing the engine to run at high rpm. But I also found out that my iscv was dead so I manually adjusted it to the right position and so far no major problems, just a bit of bogging when you let off the gas and get back on it quick.