High idle and surging

alexander · July 21, 2019

I have a Toyota aristo 2jzgte non -vvti registration 1994.[JZS147] A fault has developed regarding high idle from cold start ie instead of initial say around 1700 rpm it slowly increases instead of dropping as the engine heats up?[ once warm if rpm at idle was 1000 rpm it would clear by switching engine off/on[bringing idle to normal at hot 650-700 rpm ,but now no longer the case] On engaging auto box drive the revs drop to around 1100 rpm and the car really drives on it`s own. In park the engine surges/hunts between 1500-3000 rpm. I changed the IAC Valve ,but no difference. Toyota cannot fix as being an import, but did say it was a vacuum leak .Also car has a mines ECU. Disconnecting/reconnecting Battery no longer clears high idle either. ie ECU not relearning? Can you give me some help . Thank you , Best regards, Alex.

steve2006 · July 22, 2019

Hello and welcome to the LOC.

I also own an import but have never had a problem with parts or diagnostics.

I take it there is no Engine Management Light on?

There is a test that can be performed which injects smoke into the induction system and then you look from where the smoke is escaping indicating the location of the vacuum leak, any half decent independent garage should have this kit.

Also try spraying some “Easy Start” around all the vacuum hoses, a change in engine RPM would indicate a vacuum leak in that area.

Main one to check is the breather pipe, the valve can fail and collapse the pipe.

You could also visibly inspect all the vacuum hoses looking for poor connections and splits.

An automobile stethoscope is another useful tool to listen for a vacuum leak.

The AFM is another possible cause, if it is the hot wire type these can be carefully cleaned with a solvent.

Toyota ECUs suffer from capacitor failure which is another possible cause, from what I understand the MINES ECU is a modified Toyota unit.

Beat bet is to find a local Toyota independent mechanic, other members may have some suggestions.

alexander · July 23, 2019

Hello Steve,
Thanks for your replies.
1.Yes the EML is not on
2.The AFM-do you mean the MAF sensor.? This engine has the MAP sensor as it is non-vvti.
3.Where can I access the ECU in this vehicle ? Is it in front passenger foot well area?
4Regarding breather pipe -is this the PCV valve ?Is there a pipe underneath rocker cover ie where PCV valve is attached one pipe attaches to plenum chamber .Is there another pipe on opposite end.[I do not remember I have a soarer tt as well and I remember changing the PCV valve for a 2jz one as they suffered failure//recall allowing oil mist to get into turbo seals] I would need to take cover off engine to access rocker cover/plugs etc.
5.Regarding the IAC valve perhaps I could restrict air flow to input to valve .
6-Would EML light come on with a capacitor failure in PCM/ECU-?
7Would a faulty dump valve diaphragm cause it. I have an Apexi one

Thanks in advance ,Alexander