After removing the variable intake components in the plenum and sealing the hole i have noticed that around 35 mph my rpm's go from around 1750 and drop for a second to around 1500 then right back to 1750 ( when engine is warm).The check engine light no longer comes on and i have checked all around the intake for leaks with carb cleaner. I have removed the Idle air control valve and cleaned it as well as replced all the plugs, wires,filters etc.. It doesn't effect performance but is really irritating when it keeps doing it. Any suggestions on how to make it stop or what causes it? Also does anyone know of a Montero graveyard in Arizona? I bought a hinge there a couple years ago and have lost the web page. Thanks

Please tell us what you are driving, exactly. Make a signature.

There's a vac leak somewhere, I'll bet.

John B.

How do i make a signature? I have a 95 Montero SR with the 3.5L DOHC. Besides using carb cleaner, how can i test for a vacuum leak? I used the carb cleaner and got as much of the intake as i could and also checked all hoses.

To make a signature= click on my home on the forum page, under main configuration at the bottom of that page click on personal information edit button, go to the signature box on that page and fill in your vehicle info. also was this symptom there before you took your plenum and etc. off?

My wife was driving it when i was deployed and said she thought it was going to stall on her so when i got home i took it apart and changed the plugs, wires, etc, then it ran great except for the surging and an on and off CEL which i pulled the codes for o2 sensor and EGR valve. I replaced the plenum gasket and now no CEL but the occasional surge at 1750 RPM.If it could possibly be a vacumm leak from the plenum or throttle body i am more than willing to take it apart and replace the gaskets again. I am getting pretty good at it and can tear it all apart in less than 15 minutes now. I just dont want to spend the time and money if thats not it.

Call around local shops and see if someone has a smoke machine for finding intake leaks. If its bad enough you might can make it stumble with a squirt bottle of water if you find the right place to hit.

Take a propane torch and crack it open and play it around the intake mani joints. Idle should smooth out when you find it.

Adjust the tps.

It idles great just sitting still it only changes rpms when im driving around 30-35 mph. I have checked with propane torch and carb cleaner. I will look for smoke machine. I have been told you can also do it with a cigar? I will let you know. Thanks for the advice

you can use a cigar for this purpose <img src="/forums/images/graemlins/smile.gif" alt="" /> check this :
Finding Engine Vacuum Leak Using a Cigar