Low RPM/Cold stutter

[sparker]

Hi Guys,

calling upon the boards vast experience to see if anyone has had this problem before. As we hit winter in Australia here a week ago the temperatures in the morning have been quite cold. I am noticing (until my car warms up) that it stutters and even backfires sometimes when trying to drive at low RPM (as in, taking off from a stop). If I give it a heap of revs its ok and once warm its ok as well.

I have a couple of suspicions, but would like to know your thoughts. Firstly, its a 97 2.5l with an underdrive pulley, an intake that I made from carbon fibre and a pedro exhaust (full)

I am thinking its either the battery starting to go (low RPM, little alternator support and cold weather), spark plugs needing to change for the cold temperature or possibly perhaps my MAF sensor?

Any suggestions!

Sam

[Bladecutter]

Is your CEL light up on the dash?

Start with the spark plugs, and inspect the ignition coils for cracks/damage while you have them in your hands.

BC.

[thstone]

Based on your description I'd start with cleaning the MAF, but either way you've identified all of the likely suspects.

[sparker]

Yeah I thought MAF could be worth a try, possibly got a little dirty from the new inlet and filter. I bought some CRC MAF cleaner last night, but it was raining (and my garage is a work site at the moment) so didn't get a chance to try it out yet. Hope thats the problem!!!

If I were to look for cracks in the coils, can you describe (or show if you have pictures) the type of crack that could cause this? As in, would it be very obvious or do I need to inspect very very closely for hair line cracks?

Regards,
Sam

[sparker]

Oh - forgot to mention, no CEL and no codes when scanned. But there is certainly something going on!

Sam

[mikstew]

With my recent experience, I would also suspect the MAF, but would expect a CEL.

Note that you need to put some time/kms on the car for it to throw the CEL code, which is why your scan may have turned out negative.

[sparker]

Hmm, cleaned the MAF - problem still there.... Strangely, it does seem a fraction better though, so might just be the computer re-learning?

My next thought is some sort of leak in the inlet track, I suspect the J tube to the air/oil seperator.

Will also measure the voltage at the battery both before and after starting the car in these cold mornings to see if a combination of the battery and the under drive pulley are struggling at low rpm in the cold.

Regards,
Sam

[jhandy]

unplug your battery and let it sit, then re attach the battery. The goal is to reset your computer so that it can relearn.

You will know when it is learning, when you first start it, at idle it will RPM hunt a little. Drive it hard for a little. See if that helps.

[sparker]

Yeah might give that a shot - has been a while since I 'reset' the computer.

Thanks,
Sam

[sparker]

Ok - reset the computer, still no good. Also measured the battery this morning before starting the car (with it sitting stationary for two days) and the battery showed 11.9v (at a chilly 3.5 degrees celsius!) Once the car was started, I measured again and it read a nice 14.48-14.50 volts. Lovely!

Unfortunately though, problem was still there.... Might yank the throttle out for another clean to see if that helps at all, although I dont think that explains the backfire....

Sam

[coolbreeze551]

I am having the same issue. I even went as far as to replace the maf and it is still backfiring. I havent unplugged the battery to let it "reset" yet but I am still having the same issues even after the new Maf. Keep me posted if you find a fix.

[sparker]

I tried re-setting the computer again last night, this time I had the battery disconnected for a good hour (last time it was only 2 mins).

This did seem to fix the problem, car drove beatifully last night no backfire and much much more power.

This morning though, the problem was still half there, not as bad as other days but it was still lacking power and stuttering down low.

Problem still not solved....
Sam

[jhandy]

do you have an oiled air filter? did you try to run it with maf unplugged?

[sparker]

It is a BMC CDA, so yes, I think it might use a tiny amount of oil, but its not a cheap chinese filter dripping in oil or anything!

Havent tried running with the MAF disconnected, surely that would have to be worse?

Sam

[jhandy]

with the maf disconnected the car runs in a default air fuel map. Just like when you disconnect the battery and before the car learns...it runs default.

If the MAF is sending out crap readings, when you unplug, it will run better.

I think I can say with confidence that it is the consensus that any oil is risky and really might damage maf.

I am sure someone will speak up defending an oiled filter, but are you willing to risk a 250$ MAF sensor just because you over oiled. Besides, Power gains are very debatable that any replacement really matters.

I regret installing mine. Not because of MAF, but because my "cold air intake" really increased my intake air temp by 50 degrees when measured off the ECU. But it was such a pain to install, I dont want to undo it.

They make cone filters that are dry-oilless-reuseable-washable. I have one, works fine.

[sparker]

Appreciate your response and will try unplugging the MAF. Although I am relatively confident that its ok.

I have cleaned the MAF with proper CRC MAF spray which would remove all oil. Plus from what I hear, a new maf is less than $70US if you buy outside of porsche.

BMC is probably the world's top brand of air filters, especially for exotic cars. This filter outflows the stock piece easily and with my all carbon intake piping sealing off to the side vent, the inlet temps will not have increased at all. They should in fact drop due to the better thermal properties of carbon over plastic.

Sam

[jhandy]

there is a way to test the MAF device itself. You need a voltmeter, and a 12 volt power supply. Basically you are testing the connections, then you blow air across it, it will read out on voltmeter if good, and if you tap on it and it changes output, it is bad.

That is the idea, someone else will have to fill you in on specific methods. I found it easier to just replace it, and see.

Cleaning it does not matter, if it is going out the hair thin platinum wire is damaged or worn out. The fact that you said it ran much better with the computer reset is telling.

Do you have any codes?

[sparker]

Hi,

took the sensor out and gave it another clean on the weekend and then followed it up with a nice country drive of about 60km. (Lately I have only been doing the cold short trip to work and back - about 4km each way, car barely heats up) And it seemed to have helped quite a lot. Also put some fresh fuel in it as the last tank lasted probably about 2 or 3 months.

Car certainly liked the open road and getting up to temperature and may have helped the issue. Ran much nicer this morning on the way to work, still a slight hesitation though. Think I might order a new MAF to try anyway.

Regards,
Sam

[sparker]

oh - and no codes, but its still not 100% right.

Sam

[madmods]

Sam - I had the same issue(s) as you and ended up removing the entire throttle body assembly and deep-cleaned it. I've used "circuit board cleaner"... strong stuff and doesn't leave any residues. There is a valve in there (forgot the name of this one) that also need deep cleaning. Just make sure each parts of the assy is well cleaned and put this all back together and you'll have a brand new car bro.

After 10 years, mine was dust-oil-greese-bugs-****************e infested. It was very embarrasing to see.

While at it, you may also want to clean the airbox and conduits. Lots of ****************e residing there as well.

MAF, air filter goes after doing above.

Hope this helps