91 MR2 non-turbo high idle - Toyota Nation Forum : Toyota Car and Truck Forums

Chuckspod · 02-28-2005, 08:18 AM

Hello,

My son's MR2 5sp shredded its timing belt at 165K miles). We changed it and all of the seals using the Toyota manual as a guide.
We turned the engine over by hand several times to check the crank/cam pulley line up and everything lined up as per the manual. We had three sets of eye balls check it.

The engine fired right up and runs fine except the idle is to high. Lowest it will go is about 1300 RPMs.

We have cleaned and checked the throttle body and ISC valve, air temperature, MAP, water temperature, and O2 sensors. We also verified the EGR and its modulator.

All of the above checks were done per the manual (voltages, resistances, # of pulses per 10 sec. period......

We even tried another ECU. NO help.

If we retard the timing the idle comes down a bit but not enough and the performace goes away as one would expect.

If I block the ISC orfice in front of the butterfly in the throttle body the idle does drop to normal. This is what got us checking all of the aforementioned items in the first place.

The ISC has the normal resistance and functions as per the checks in the book with the throttle body off of the car. The voltages from the ECU to the ISC show a change as the engine warms up and the idle speed drops off but they never get near the full close amount of 0 volts and 12 volts.

If the cam timing is off 1 notch of the timing belt would this cause what we are seeing? If the cam timing is off, which way should the cam/belt be moved? Advance the cams or retard the cams?

Thanks!

***MR2Jedi*** · 02-28-2005, 06:33 PM

don't want to sound like a smartass but theres no mention of adjusting the idle with the idle screw on the throttle body..

Chuckspod · 03-01-2005, 07:21 AM

Thanks, but thats not it.

jtl · 03-01-2005, 07:57 PM

I have gone through the same things you have (i.e. rebuild engine and new belt, etc.) and get the high idle still. I did all the checks you did and they came about on the mark but the idle stays around 1200. I also checked for proper functioning of the air conditioning idle up switch (VSV). Took it off and bench tested per manual and it checked out ok (you might want to try that as well and check it for leakage).

I don't know what it could be but I have heard this story a lot on 91 na's. Maybe it could be that the vacuum lines are all just too old and have become porous which could result in some leakage and affect idle rpm. I haven't checked the MAP yet either but I'll give it a go as well. Maybe I'll try replacing the vacuum lines (its a cheaper try at fixing this). Let me know if you make any progress.

uribemr2 · 03-05-2005, 05:09 PM

I had 4 machanics and the dealer check my 91 mr and they all said that it was the ISC Valve but I change 3 of them two used and one new and still same shit. sorry that I can be of help to you but try to change the ISC see if that works for you.