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Surging on acceleration. #1106216 04/14/21 11:19 PM
Joined: Aug 2020
Posts: 185
T
Trailmonkey Offline OP
Wheeler
Just started this and getting worse the more I drive it.
Stop at the store and it drove fine, get back in and start it up, seems the idle is a bit off but ok.
As I take off it almost feels as if the trans is slipping or its cold, give it more throttle and not much happens, got upto maybe 40mph and bam it hits warp speed and is clear, I had it at about 45-50% throttle when it gets back to normal.
Doesnt do it all the time but when it does its after it was shut off and restarted.

Throttle position sensor ?
Idle control unit ?
Or possessed ?


91 (Gen1) Monty, 3.0L V6, Auto 4 Door.
Disabled Driver.
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Re: Surging on acceleration. [Re: Trailmonkey] #1106219 04/15/21 04:43 PM
Joined: Dec 2007
Posts: 2,331
Mudraider Offline
Body Damage is Cool
Well, if you clean the MAF with a spray chemical, make sure it's Mitsubishi safe.


89 SWB, V-6 5SPD, OME Shocks, 16.5X37's, 2"BL, SR axle, Gen2 brakes, Lincoln w/Superwinch
Re: Surging on acceleration. [Re: Trailmonkey] #1106221 04/15/21 05:39 PM
Joined: Aug 2020
Posts: 185
T
Trailmonkey Offline OP
Wheeler
So you think thats the cause ?
The air flow sensor at the air filter looked good the last I seen it.


91 (Gen1) Monty, 3.0L V6, Auto 4 Door.
Disabled Driver.
Re: Surging on acceleration. [Re: Trailmonkey] #1106222 04/16/21 08:56 PM
Joined: Aug 2020
Posts: 185
T
Trailmonkey Offline OP
Wheeler
What ever it is, it does it for a short time then totally clears up.
Makes me think one of the two, the ones on the throttle itself.
Would the Idle Control Unit make it so as you give it some throttle input it has the ability to give a lower perceived throttle, fluctuate (surge) then opps my bad go back to normal ?
Or the Throttle Position Sensor simply malfunctioning for a bit then goes back to normal ?
After that its fine. Shut it off and it may or may not do it again.

I actually thought the trans may be slipping till this last time, and had the throttle opened up a good bit and when it cleared up jumped and took off as I had the pedal down more than normal. No slipping, thats throttle related.. hmmm

So now I'm asking the Montero Gods of Knowledge... is it my rear taillight bulb is out or one of the 2 mentioned culprits ? Haha

Last edited by Trailmonkey; 04/16/21 08:58 PM.

91 (Gen1) Monty, 3.0L V6, Auto 4 Door.
Disabled Driver.
Re: Surging on acceleration. [Re: Trailmonkey] #1106236 04/20/21 12:11 AM
Joined: Oct 2020
Posts: 12
L
Lev_from_CA Offline
Need a Spot
Stumbling/surges sound like fuel issues. Old or watered down fuel, a clogged up fuel filter/in-tank strainer or failing pressure regulator. A failing fuel pump may also cause stumbles/surges if it's struggling to keep up with pressure demands, although that tends to be most noticeable at higher RPM.

Re: Surging on acceleration. [Re: Trailmonkey] #1106238 04/20/21 04:38 PM
Joined: Aug 2020
Posts: 185
T
Trailmonkey Offline OP
Wheeler
And after about 15 seconds totally clears up...
In park I reved the motor up to 2000 rpm, ran like crap, low power and wanting to go up and down in rpm.. not changing the throttle input any it all of a sudden clears up and i had to let off the throttle to keep it from going over 4000 rpm, ran just fine after that.


91 (Gen1) Monty, 3.0L V6, Auto 4 Door.
Disabled Driver.
Re: Surging on acceleration. [Re: Trailmonkey] #1106239 04/20/21 04:40 PM
Joined: Aug 2020
Posts: 185
T
Trailmonkey Offline OP
Wheeler
Been getting about 13 mpg also.


91 (Gen1) Monty, 3.0L V6, Auto 4 Door.
Disabled Driver.
Re: Surging on acceleration. [Re: Trailmonkey] #1106241 04/20/21 06:19 PM
Joined: Oct 2020
Posts: 12
L
Lev_from_CA Offline
Need a Spot
Yep, IAC could be acting as a vacuum leak causing the low RPM stumbling and hunting. Low fuel mileage and stumbling at low rpm/at startup could also be a plugged up fuel filter that the fuel pump takes a while to build pressure through. I suppose a failing FIAV can also appear as a vacuum leak, but that seems less likely in your case (stumbling while both warm and cold idle).

To check if the IAC is implicated, you can steer lock to lock while parked and watch how RPM reacts, it should increase matching the smoothness of your steering (steer quickly, RPM should rise quickly, steer slowly, RPM should rise slower). I remember you had AC removed, but steering exertion should also trigger the IAC to compensate for increased load. If you have a multimeter, you can check the resistance of the coils and measure the switching frequency during operation (iirc, 25-35 counts at idle, 65+ counts with AC/steering on). To test the IAC while warm, you can take it out, warm it up with a hair drier/heat gun (be conservative), and then test the coil resistance again.

Re: Surging on acceleration. [Re: Trailmonkey] #1106242 04/20/21 07:17 PM
Joined: Aug 2020
Posts: 185
T
Trailmonkey Offline OP
Wheeler
Mudraider said to just unplug the Idle control unit all together and set idle with the stop screw. I'll do that and replace the TPS..
Fuel filter has less than 500 miles on it but not checked the pump yet. But its evident its been replaced or at least looked at as the little hatch has been taken off and reinstalled at some point.

Just odd how it clears up and starts working. I know these dont get the best fuel mileage but it should be getting at least 15+.
Just in case I'll replace the O2 sensor just so I know its fresh.


91 (Gen1) Monty, 3.0L V6, Auto 4 Door.
Disabled Driver.
Re: Surging on acceleration. [Re: Trailmonkey] #1106245 04/22/21 04:59 PM
Joined: Aug 2020
Posts: 185
T
Trailmonkey Offline OP
Wheeler
Simply unplugging the Idle control unit fixed the problem.
Set the idle screw till she idles at about 800 rpm, put it in gear and goes down to about 600 rpm or so the tachometer says.
The numbers sounds low to me but it has alot better idle quality and idles lower, has a more responsive throttle and is a bit more peppy.
Just feels better, I'll bet it will get better mpg now also. I hope.


91 (Gen1) Monty, 3.0L V6, Auto 4 Door.
Disabled Driver.
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