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3.0l V6 Idle Problem #1104049 01/05/18 07:02 AM
Joined: Jul 2014
Posts: 22
AlexM Offline OP
Need a Spot
So I was having some idle issues again (after about 2 years of no idle problems) with my 1990 Montero. I figured I'd try the solution on the Solving the 3.0I V6 Idle Problem page. I removed my throttle body, gave it a good cleaning, and put it back on (with a new throttle body gasket) and fired it back up. The problem didn't go away, but the cleaning sure made it more consistent. Before, it idled high (around 2k RPMs) until it warmed up, then it would either stay idling high or start bouncing rhythmically between 1300 and 2200 RPMs. Now it starts doing the idle bounce before it is fully warmed up, and is more precise in both the RPM levels and the rhythm. The engine runs fine when driving, but sure doesn't like to idle quietly.

When the engine is warm, and I disconnect the MAP (Volume Air Flow?) sensor, then it goes into a closed loop and idles fairly normally and the CEL comes on. But I don't get any CEL light when it's doing the idle bounce.

Could I have introduced or exacerbated a vacuum leak when I "fixed" the throttle body? Is a vacuum leak or extra air intake the cause of the 3.0I V6 Idle problem? Could it be my IAC? I took it and the TPS off when I cleaned the Throttle body. What other problem could mimic the dirty throttle body problem? I'm kind of stumped as to what my next step should be in trying to diagnose this issue. Any insight is appreciated.


Limited Mechanical Skills
'90 Montero RS 5-speed
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Re: 3.0l V6 Idle Problem [Re: AlexM] #1104052 01/06/18 03:21 AM
Joined: Feb 2005
Posts: 7,367
rxinhed Offline
Trail Leader
Section 14 of the FSM would be a good read

Re: 3.0l V6 Idle Problem [Re: AlexM] #1104053 01/06/18 05:49 AM
Joined: Jul 2014
Posts: 22
AlexM Offline OP
Need a Spot
Thanks, I'll take a look.


Limited Mechanical Skills
'90 Montero RS 5-speed
Re: 3.0l V6 Idle Problem [Re: AlexM] #1105117 07/02/19 04:59 PM
Joined: Jul 2018
Posts: 1
arevv Offline
Need a Spot
Hey Alex, did you ever find a solution to this issue? I have the same symptoms on my 91 and have been working through the FSM to diagnose. I replaced the IAC, checked the MAF with a multi-meter, checked the ECU which was rebuilt (Had a rebuilt sticker but haven't opened it to inspect) and checked for vacuum leaks...no dice so far. Tonight I'm going to test the TPS and dig a little deeper for vacuum leaks.

For reference, the issue started at the tail end of a 500-mile round trip which included some offroad driving and a few deep puddle crossings. Issue first appeared when I was pulling in my driveway at the end of the trip.

Re: 3.0l V6 Idle Problem [Re: AlexM] #1105127 07/14/19 01:34 PM
Joined: Dec 2007
Posts: 2,269
Mudraider Offline
Body Damage is Cool
In mitsubishilinks.com there is a book called the Driveability Manual. Have you looked at it? Hopefully the throttle body itself hasn't "wore out". A common fix for the floating idle when it is the throttle body, is to make a block off plate for the bottom of the throttle body.

89 SWB, V-6 5SPD, OME Shocks, 16.5X37's, 2"BL, SR axle, Gen2 brakes, Lincoln w/Superwinch
Re: 3.0l V6 Idle Problem [Re: Mudraider] #1105133 07/18/19 05:10 AM
Joined: Mar 2003
Posts: 2,324
KrzyDav Offline
Body Damage is Cool
I think the blockoff plate that the youngsters are putting on Eclipes might fit 90-94 TB. I don't know the name of the place that sells them I know if its an 89 you have to make it yourself.

dave h.
'89 Raider V6 5spd;Aisin Hubs;; Gen2 LS: frt. brakes, rear coils;U.C.arms;R.trailing arms;idler arm; rear LSD axle w.disc brakes ;2 battery system for Dog's fan; relocated ECU; custom bumpers;J.Baker receiver;Conferr roofrack; t-bar crank.

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