1995 MK1 revving too high randomly

[Elmar]

Can somebody give me advice on this please?

For the last year randomly when I take my foot of the accelerator and I am at a stand still
the engine will drop to 1500rpm and hold there for about 8 seconds and then drop to 800 rpm.
I have had the car checked for vacuum leaks by 2 different mechanics; I have bought a 2nd hand mass air flow meter and that made no difference.
I also bought a 2nd hand inlet manifold with all the sensor’s attached and that made no difference.
I’m at my wits end and don’t want to spend any more money on the car.
The other day I was going down a long hill and I took the car out of gear she coasted down the
hill at 1500rpm all the way when I stopped the car at the traffic lights it took 8 seconds for the car to drop to 800 rpm.
I went home and got back into the car 5 min later started her up and all was fine no high revs. Its driving me mad.

[pjmazda]

http://forum.miata.net/vb/showthread.php?t=434325

Have a look at latter, sounds just like your symptoms - I.e. idle control valve

[MX5Spares]

We have good used valves for sale.ROBERT 086 8226506

[sidewaysreilly]

what year and what engine size?

[Elmar]

Thanks for the replies

Its a 1995 1.8

[Elmar]

Sorry I should have put this in as well.
The car was running fine until the engine went on me 1 day
I got a complete 2nd hand engine from Traynors up north.
When I got the car back from the mechanic it started hunting at the traffic lights
I bought the car back and he said he would put my original idle control valve on.
Got it back and the hunting had stopped but randomly the car would rev at 1500rpm
at traffic lights. I then bought in from the UK a complete inlet manifold with ICV etc attached
and went to a different mechanic. He tested everything and put on the inlet manifold
things were good for a bit but then the rev problem started again. People keep saying
idle control valve but can I be that unlucky and have 3 of them not work for me especially
if my original 1 was fine be for I changed the engine?I have to say if I had my time back and knowing what I know now I would have dumped the car in the breakers and bought 1 of internet of the same year it would have cost me a lot less in the long run.
1 other thing during the summer the ERG valve pipe connected to the exhaust manifold had come lose I tightened the bolt backup but the was no washer on the pipe end just a sort of metal ring on the outside of the pipe which was part of it I thought the lack of a washer was a bit strange.

[sidewaysreilly]

Do away with the erg completely and blank off the manifold(s). Waste of time and wont affect emissions.
If the engine was from a later mk1(will have ordinary bolts holding down the rocker not the earlier chromed ones) it will be OBD2. Some of the sensors will not be compatible. I had the same problem and had to use all origional sensors , oil pressure, coolant temp and the throttle body too before the bollix would idle properly.

Try this and report.

[rhysmate]

i dont suppose it would be something to do with the idle setting? you know the old paper clip in the diagnostics connector trick?

http://www.miata.net/garage/KnowYourCar/S7_Idle.html