Idle is not consistent

[cdcarson]

Greetings,

I have a Mazda Protege ES 1.8L Automatic Transmission. I have about 108,000 miles on it.

The engine is not idling like I would expect it to be. It runs at about 1000RPM at first when cold and then tries to idle about 800. However it varies from 400-800.... However it will not sit constant for more than 2-5 seconds. At normal driving speeds the engine runs fine.

Two things effect the idle.

1. When I turn on the A/C it will jump from 500rpm up to 800 for a few mins. Then it comes back down to ~400-600rpm eventually.

2. If I turn the steering wheel engaging the power steering the engine around ~500rpm drops almost to ~400 and almost stalls.

Any Ideas. Their is no Check Engine Light.


Best Regards,
Chris

[peajay]

the a/c power surge and power steering load drop are normal, i would suspect maybe your iac starting to fail or a small vacuum leak.

[cdcarson]

What would be the best way to find a vacuum leak? All hoses look good and are connected.

Thanks,
Chris

[gone_fishin]

As Peejay said, those idle drops are unrelated.

Your issue could be due to a number of things, but the most likely culpret is either a blown intake manifold or throttle body gasket.

How to Check: Get some carb cleaner and spray it over where the intake manifold ports meets the head. Likewise do this around where the throttle body port meets the intake manifold. If you hear a sudden pitch in idle, you'll know it's that gasket.

If it isn't either gasket, check your intake track for vacuum leaks.

[cdcarson]

Thanks for your response. I'll grab some carb clean on the way home and give it a skirt. Hopefully it is something simple to fix.

Thanks,
Chris

[gone_fishin]

Not a problem. Let us know how it turns out.

[Protegebuddy]

What would be the best way to find a vacuum leak? All hoses look good and are connected.

Thanks,
Chris


Have to do a smoke test to find a vaccum leak.

[Not Jo3L]

Sounds like the same problem i have with the same car and the same miles..hehe

but i think mine is due to a blown pre-cat

[red99pro]

seafoam that hoe

[cdcarson]

Hey Guys,

Thanks for your responses. I think I'm making some troubleshooting progress. But I don't have any definte answers yet.

When I first got the car about a month ago the MIL was on and the code was I found p0106(BARO circuit performance problem). I found that the EGR boost sensor solenoid vacum hose that connects to the intake manifold was disconnected. I reconnected it cleared the code and things seemed normal for a while.

Then the engine started to run rough at idle as I've already said above in the post.

I have offically baptised my intake manifold and vacuum hoses with carb cleaner without any results. I then started thinking about the other comments in you guys have posted. I also got out the service manual and followed the recommended proceedures for a rough idling engine. I disconnected the IAC and the engine stalled as expected. I also measured the resistance and got the expected ~8.2ohm. So I think that is fine. The throttle body with Gasket also looks good.

I have since then had the two following codes:
P0420(Catalys efficent low-bank 1) and tonight I've received P0171(Fuel Trim system to lean)

These make me think I could have bad O2 sensors, or precat? I think this due to the fact the two O2 sensors monitor the exhaust before and after the precat. And the computer takes the o2 sensor values and calculates fuel/air mixture.

How can I best determine what component is bad? Please point out anything that I might be missing...


I've recently got a OBDII interface for my laptop so I can read all the values in realtime. One thing tonight I found that O2 Sensor 1 in Bank 0 seems to read 0.00 volts for brief moments during the rough idle which is about 523rpm. And then it is fine and goes between .1-.8

Thoughts? Questions? I could post some Logs of OBDII data etc..

Maybe all I need is some seafoam ;-)


Thanks Guys,
Chris Carson

[red99pro]

too lean= vacume leake = bad idle

[peajay]

You could have an oxygen sensor starting to go, cat efficiency codes are alot of times related to O2 sensors taking a shit. plus your 0v reading doesnt seem too promising

[CaliAv8r]

ok this is my problem with rough idle

its fine when I turn it on and just leave it at idle. But once I touch the throttle and it goes back down, it starts to idle rough like it wants to die. Sometimes it dies, other times it just idles really rough till I push the throttle in.
I checked the code and P0118 came up, something about engine coolant temps. But what would that have to do with rough idle? did I blow a head gasket or something?

I am going to get a compression and leak down test tomorrow so yea...hopefully its not too bad...

help!

[red99pro]

excuse me, but gone fishin u did a MSP swap in a 99-00???

[CaliAv8r]

UPDATE!!!

I switched out the instument cluster to the stock one. It fixed the problem, man sometimes it seems that anything will work...

[gone_fishin]

excuse me, but gone fishin u did a MSP swap in a 99-00???

yes I did

[red99pro]

I never knew(eek2)