John Speake

It almost sounds like and igntion lead problem, with gearbox in neutral, slowly increase engine rpm, there should be no noticeable engine vibration.

A MAF out of spec would be very unusual at those miles. The only cars that age their MAFs so quickly come from places like Hong Kong in my experience. And if you car has O2 loop then the long term LH adaptation will compensate for moderate ageing.

Randy V

As previously mentioned, the MAF is a maintenance item, requiring replacement at some interval - not sure what that is exactly.

John Speake

80-90k miles would be typical for throttle response and max power to be blunted somewhat . But it shouldn't affect part throttle and idle running due to the LH adaptation.

A rough idle with vibration suggests ignition leads or an injector not flowing properly. But in this case the OP said he had had the injectors cleaned.

Bertrand Daoust

Thanks John,

Ignition wires, rotors and caps were change about six years ago. I checked all the wires and they're all at the right place. Coil wires cleaned too. But can double check. Spark plugs are only one years old.
Injectors cleaned this spring. I can hear them all clicking.
When I slowly increase engine RPM, the vibration stops. Like I mentioned, it's just like it is idling just a tad to low.

I will check with another MAF this weekend (probably) and see how it turns out.

Both the vibrations and low idle when warm is worst this year.
The dropping idle at a complete stop is new this year. Just as the car (LH maybe )can't maintain the correct idle for a very short period of time before taking control again and bring it back to about 625 RPM. Which is still a bit too low.

John Speake

OK, just a lumpy idle with some vibration..... OK on the ignition system.

You could try two things at the same time..... a battery disconnect and a way of checking if the O2 sensor response is slow.

Disconnect battery ground strap under the edge of the tool tray. Then disconnect the O2 sensor at the 15mm diameter round rubber connector on the floor in front of the CE panel. Then reconnect the battery ground and start the car. See how it runs.

This process does two things - it clears the adaptation parameters which are stored in the LH ECUs SRAM, and it also forces the LH ECU to recognise the disconnected O2 sensor. This makes it default to the mid range of the O2 loop.

It's worth a try, and doesn't cost anything :-)

Bertrand Daoust

I'll try that for sure and get back to you.

Thank you very much John.

Edit: Can I drive the car for a little while with the oxygen sensor disconnected?

Bertrand Daoust

Ok I tried disconnecting the O2 sensor and...
BINGO!
Thank you John.

Idles perfectly. No vibration. Smooth like it should be. In park and in gear.
And it didn't drop below 650 RPM at a complete stop, in gear, when I drove it. I didn't drive it much but it ran better than last weekend.

I guess I need a new O2 sensor. Right?

A question, can I drive the car for a while with the O2 sensor disconnected?

Also, what is the function of the O2 sensor in our car?
If I disconnect it and the car runs great, why or when would it need one?

I know it's maybe a dumb question but always willing to learn!

Thanks again.

jcorenman

Cool!
Yep.

Yes, if it runs fine without it then it is OK to run without it.

The LH uses the O2-sensor to make to adjustments your fueling as the engine runs. So if the MAF is aged and reading low (lean), then the O2-sensor will detect that lean mixture and add more fuel (by increasing the injector pulse-width). It does this as your drive, and then remembers that correction-- this is the "adaptation" that is saved, and gets reset when the battery is disconnected.

So if the MAF, LH etc. is all working properly, then the O2-sensor doesn't do much adjusting, and the engine runs fine with or without. But if the MAF is out of calibration then the O2-sensor is needed to correct the mixture (within limits). But conversely, if the O2-sensor itself is whacky and not reading correctly, then the adjustment will be wrong and will throw the mixture off instead of correcting anything.

The other issue is cat's, if you still have them then you need the O2-sensor to keep the mixture around the ideal 14.7:1 ratio. So with cats I would replace the O2-sensor sooner, rather than later.

Cheers, Jim

Bertrand Daoust

Yes I have the stock cats so new O2 sensor on the way.

Thank you Jim for the clear explanation.
Very appreciated.

John Speake

OK Bertrand, that's a good first step in diagnosis. You could now try reconnecting the O2 sensor - keep the battery ground connected, engine stopped. Then run the engine up to temperature, remembering that until the water temp gets near normal, the O2 loop isn't activated.

It is possible that just clearing the old adaptation values is all that was required. I had a GTS here a couple of weeks ago, using lots of fuel, rear of car black etc. Clearing the adaptation by a brief battery disconnect (say 5 seconds) and after a minute or two it was running sweetly again. The adaptation can often get iitself in a mess...

Bertrand Daoust

Thank you John.

I had the battery disconnected (with the O2 sensor connected) a few times in the past and the idle was not as smooth as it is now. At least not since many years.
I think that tends to say that my O2 sensor is not reading right.

At least that's what I think of all this.

Thanks again guys for all your help.
Very appreciated.
Love Rennlist!

Andre The Giant

Hey Bertrand, I'm glad to hear that you have found the issue and it's not the MAF . You will at least be able to enjoy riding again. Maybe we can schedule a small trip together sometime.

Bertrand Daoust

Thank you André.

Of course. How about next weekend with Rennsport?

Not 100% sure yet, but I might join them for the coffee run.

Bertrand Daoust

Went for a close ride tonight and the car runs better than ever!

Let it idle for about 30 minutes.
This car as NEVER idle that smooth since I bought in 2005.
O2 sensor is disconnected.

Don't remember reading something on the O2 sensor doing this!
Well...

John Speake

It MAY be that the O2 loop in the LH ECU is faulty, even if it defaults to mid range when it detects a disconnected O2 sensor. This partial failure of the LH is uncommon, but I have seen it several times.

Change the sensor first (good preventitive maintainance) and see if the fault is cured.