Idle problem

[roaming knome]

Hello all,

I recently replaced my ISC (Idle Speed Controller) in my 1989 gen 1 Montero because when stopped at a traffic light or stop sign the Montero would die or have very sporadic and rough idle either about to die/stall or want to power surge as if my foot was on the gas pedal. After replacing the ISC it does drive better, throttle seems to roll on smooth and no more stalling or inconsistent idle at stops. However on first start up (cold engine) idle is 1800-2000 rpm and after warm up it drops to the 1100-1400 rpm range but it never really drops below that and the Haynes manual (which is the one I have) has 700 +/-50 rpm for my 89' Montero with 3.0L V6 with auto trans.
That is not the only problem either, once the rpm get to 2500 or accelerating up to any speed the check engine light comes on and stays on until rpm's drop to about 2300 or below. The Montero otherwise drives fine but I would like the idle to be within spec and the check engine light to be off unless there is a serious problem which there might be right now

Any and all help would be greatly appreciated.

 

[off-roader]

Hello all,

I recently replaced my ISC (Idle Speed Controller) in my 1989 gen 1 Montero because when stopped at a traffic light or stop sign the Montero would die or have very sporadic and rough idle either about to die/stall or want to power surge as if my foot was on the gas pedal. After replacing the ISC it does drive better, throttle seems to roll on smooth and no more stalling or inconsistent idle at stops. However on first start up (cold engine) idle is 1800-2000 rpm and after warm up it drops to the 1100-1400 rpm range but it never really drops below that and the Haynes manual (which is the one I have) has 700 +/-50 rpm for my 89' Montero with 3.0L V6 with auto trans.
That is not the only problem either, once the rpm get to 2500 or accelerating up to any speed the check engine light comes on and stays on until rpm's drop to about 2300 or below. The Montero otherwise drives fine but I would like the idle to be within spec and the check engine light to be off unless there is a serious problem which there might be right now

Any and all help would be greatly appreciated.

I suspect the previous owner or mechanic adjusted the base idle or you have a vacuum leak in one of the many hoses in/around your intake manifold.

Also the 89 Factory Service Manual is available for download from mitsubishi links dot com.

 

[roaming knome]

Thanks for the reply/advise! I read it could be a vacuum leak but that doesn't seem possible as it did not have high idle before I changed ISC. The second I first started the engine with the new ISC it immediately started with the high idle.
I will consult the factory service manual and see if there is any new/different information from the Haynes manual that I have.
Thank you again for the info, I appreciate it.

 

[off-roader]

Thanks for the reply/advise! I read it could be a vacuum leak but that doesn't seem possible as it did not have high idle before I changed ISC. The second I first started the engine with the new ISC it immediately started with the high idle.
I will consult the factory service manual and see if there is any new/different information from the Haynes manual that I have.
Thank you again for the info, I appreciate it.

You didn't have a high idle present probably because the ISC was bad which forced the idle down. Then once it was replaced the idle went high to we're it was set by the prior owner or mechanic to minimize the engine dying from a low idle brought on by the bad ISC.

 

[shov3lbum]

Definitely could use an ECU memory wipe sounds like. Was the battery dis-connected for more than 5 mins (or 10 mins, whatever it is) anytime after the new part install? If not that's your first place to look. The ECU will then start with the idle air control at the base setting and increase the valve until the idle evens out. At least in theory...

 

[scrubber3]

Best to disconnect the battery before switching out the IAC. I'm sure by the time you Connect the new IAC the ECU would have reset itself.

 

[roaming knome]

Thank you all! I disconnected the battery for approx 15 minutes, reconnected and fired it up. It started at about 1500 rpm so about 500 rpm less. I then drove it around the block to warm it up and when I parked idle as back down to 750-800 rpm. I was very excited to see the low idle numbers and also how smooth and consistent the engine sounded! Thanks again!
Also just before replacing the ISC, I performed the arduous task of replacing the crankshaft bolt. It snapped on me 2 weeks ago on my way to work! I made a little jig to drill the rest out straight with out any thread damage. Managed to get it fixed in 1 whole day! What a PITA!!! But I am very proud to say that the Montero is running better than ever!

 

[scrubber3]

AWESOME!!

 

[shov3lbum]

that's awesome, good to hear! And a crankshaft bolt snap?! Wow, did the crank pulley still stay on or did the whole front end of the engine fall apart?

 

[roaming knome]

Yes Scrubber3! Yes it is, I love my Montero! I think they are a very well built and capable vehicle and yet people still underestimate them.

Hi shov3lbum, I was actually making a right hand turn at a stop and snapped when it shifted from 1st gear to second so I was not moving very fast and the level that the Montero was performing before the catastrophe was below mediocre at best so the break maybe happened at around 2300 rpm? As soon as I heard the break the engine immediately died, I threw it in neutral and pulled over and parked. luckily and fortunately no damage was done other than: chipped crankshaft woodruff key and stripped pulley key way channel. the pulley was still on and held in place by all 3 belts.
I ended up filling the pulley ID with weld and reground the key way with a file and dremmel tool. I saved my ******** big time! I did order a new harmonic balancer pulley which I have now and still need to swap, maybe I will get to it this weekend. The bolt snapped inside the crank where the threads start. This made it much easier for me (in my opinion) to extract. Because the crankshaft has a counter bore relief cut the streads do not start until about 10-12mm in, so that is when I got the idea to make a center drill guide out of a piece of 3/4" steel round stock.
I forgot to mention that I have a mini workshop :wings:
So I turned the ID to fit inside the counter bore snug but still easy to pull out and then started with a 1/4" hole and drill to start my hole. Once I drilled the rest of the bolt through I through on the bolt extractor. No budge and a whole LOT of extractor flex so modified the drill guide to 5/16" got a larger dia. extractor, same result! By that time I wanted to cry. But I held my own and just had to think. I finally came to a realization that it's 2012 now and that bolt has been in the same place, static since 1989!!! I had to be stronger and smarter than the bolt, since I already had the biggest extractor that would fit in the hole, at this point I measured the new bolt and crunched some basic numbers and enlarged my guide to 12.5mm and basically drilled the bolt body away so the only thing left was similar looking to a heli-coil. I then ran a tap through to break up the threads and WALLA!! No thread damage!
Now I really regret not taking pictures of my proud moment, but I can't even begin to explain how frustrating that job was. A camera was the last thing on my mind. in fact the only object that came to mind during the projects was a very large hammer:ar15:
Anyways I am felling much better now and I love my Montero again, all I have to say is that I really and I mean REALLY hope that I do not have to do that again.

Adrian.