RPM's fluctuating after timing belt change.

[tradosaurus]

I have a 2000 Mazda Protege 5 speed with the 1.6L DOHC ZM engine.

I recently changed the timing belt and all associated items (water pump, seals, tensioner pulley, idler pulley) and after starting it up it sounded smooth but upon warming up the RPM's would fluctuate between 700 RPM to 100 RPM and sometimes the engine would stall. This was only after the engine was warmed.

I followed the service manual for lining up the cam shaft and crankshaft marks and with a two wrenches and a vise grip held the cam shafts from moving during timing belt install.

I heard that air bubbles in the coolant system can cause this but after installing a new thermostat (after timing belt change) I'm pretty sure the air bubbles are out.

My order of diagnosis before tearing everything down to get to the timing belt is:
1) check timing with timing light
2) Check for error codes
3) Clean EGR and IAC.
4) Check for vaccum leaks (visual inspection of main inlet hose seemed good)
5) Clean the crankshaft sensor and check gap.

The car ran great before the timing belt change so logically I would think it is off a tooth since I haven't messed with the EGR or IAC and if there were vacuum leaks it would have been there before the timing belt job.

Any other input or ideas would be welcome.

 

[MazdaSport20]

..Idle air control valve..
Mine was doing that and after I found one at a junkyard from a 626 the problem went away

 

[tradosaurus]

That's interesting. Is it a coincidence that the IAC would have a problem right after I performed a timing belt change?

 

[JReichle1]

What brand timing belt did you use? I used one off ebay and it was too tight causing misfires... Are you sure the engine was timed correctly?

 

[tradosaurus]

Timing belt is a Gates. I rechecked the timing belt installation and it was good.

There is no way to adjust timing that I know of but the timing came back at spec. (10 BTDC).

I think the fluctuation was a result of washing down the engine before the timing belt change. It could have caused a mechanism or valve to function improperly.

I've checked all sources of vacuum leaks and replaced any issues.

It use to stall but after replacing the intake manifold gasket now it just fluctuates slightly at idle once warmed. I'm hoping in time this will smooth out.

If not then I will replaced the IAC and idle positioning valve.

 

[JReichle1]

You might want to clean off your mass air flow sensor... My car's idle fluctuates when the MAF gets dirty...

 

[tradosaurus]

Yeah, I did that also.