I have a 1991 GD Mazda 626 2.2ltr auto sedan (NOT turbo) - has about 200,000 klms on clock
The engine revs by itself between 500 > 2000 revs. This is not on a cold start but a hot start after the motor has been off for 15-20 mins but still hot
It revs up and down on idle or driving but after 10 mins driving revving problem appears to go away or just up and down from 500 > 800 revs
I noticed (with bonnet /hood up) that the accelerator cable does not move when auto revving happens
What might be causing the problem
- O2 oxygen sensor?
- air flow meter?
- idle valve?
- vacuum hose leaks?
Is this a common problem with Mazda 2.2ltr injected motors? If so whats the common cause?

I checked the air filter (changed 22 months ago) looks fine
I checked the EGR valve at top of tappet cover - seems tight enough - I pulled it off and engine stopped - put back on a motor kicked over OK
Put injector cleaner additive in petrol tank
Fuel filter and plugs changed 22 months ago
Oil level fine
Radiator coolant and temp fine
No smoke from exhaust pipe after revving manually
Accelerator cable at engine top seems fine and not frayed
Did NOT check for air sucking noised at vacuum lines but they appear to be connected

thanks
Speedy

 

Speedy: you need to check for vacuum leaks, and clean the MAF sensor with a MAF sensor cleaner.
You may also benefit from cleaning the throttle body.
It is possible that the ECT sensor (Engine Coolant Temperature sensor) is faulty.
That thing on top of the valve cover is the PCV valve, not the EGR valve. Cleaning the EGR valve could also help. Look for a tube coming out of the exhaust and going back to the intake manifold area. that's where you find the EGR valve.

 

Where do I find the MAF (airflow sensor) and ECT sensor?

I don't have the car at the moment my daughter is driving it so I can't look for it till I get it back

 

Under the hood.....sorry, I am picking the low hanging fruit again.

I suggest you buy the Haynes Manual (Amazon.com). It really will help you a lot and it is worth the $20.
The MAF sensor is located after the air filter at the start of the intake hose. The ECT sensor is near the thermostat.


Tan

 

thanks Tan

I'll have a look when I get the car off my daughter - she keeps taking off with it

I won't buy the manual because I'm going to dump the car for parts in about a month or two after the rego runs out

 

by 'dumping the car', do you mean selling or scrapping?

Really sounds like it wouldn't take much work or money to straighten out the idle issue. At 200,000km, the engine still has life. The body, that can be a whole other story...

Have you checked the intake hose for cracks? Have you checked transmission fluid?