Cold Start problems

[Rui725]

Hi all,

My 1998 986 has been experiencing start up problems when the engine is cold. To be exact, the car has to be left over night without being driven. Symptoms:

1. rough engine start

2. Lights on the dashboard blinks (like a shortage of power)

3. no power when I hit the gas (moving it out of the garage).

4. If left undriven for 2 or more days, the RPM will bounce up and down and feel the car lose power when trying to warm up. and then it'll shut down completely.

5. These symptoms usually go away after I restart the car 2-3 times.

6. Once the car is warmed up and driven, it drives perfectly. any subsequent restarts after the engine has warmed is perfect.

7. No check engine lights have popped up.

The car is in the shop at the moment. The mechanic guessed it was either 1. fuel injection pump or 2. MAF. 3. Fuel filter?

Any postulates? I'm guessing the MAF as a CEL was on for it 2 months ago, but I decided to let it go to see if the light would pop up again. The car also has a history of O2 sensor CEL's. I know I'm not provding any error codes, but from these symptoms i'm hoping I can find out what is possibly wrong.

-Rui

[zodman]

Any smoke at start-up?

Sometimes an RPM bounce can mean several different things, including the MAF. But it can also be a vacuum leak, a dirty throttle body, a bad AOS, or even a combo of all.

When my fuel-pump went, it didn't start. It would turn over, but it wouldn't start. As what I've gathered here on the board, the fuel filters are pretty hardy.

The cheapest route at the moment, would be to clean the MAF and the throttle body. If it clears up, but returns, replace the MAF.

I replaced my AOS b4 any symptoms such as lots and lots of smoke appeared. Cleaned the throttle body and the MAF at the same time as well. Had no error codes to speak of, but the RPM bounce went away.

You can DIY the MAF/Throttle Body/AOS yourself, but I would let the mech. do the Fuel Pump as it is located in the fuel tank.

According to some info I have, a fuel pump will fail earlier if the fuel tank is ran too many times at a low level.

Edited November 25, 2009 by zodman

[Loren]

Even thought you have no CEL - you should have the fault codes read. Look for pending faults.

[Rui725]

Any smoke at start-up?

Sometimes an RPM bounce can mean several different things, including the MAF. But it can also be a vacuum leak, a dirty throttle body, a bad AOS, or even a combo of all.

When my fuel-pump went, it didn't start. It would turn over, but it wouldn't start. As what I've gathered here on the board, the fuel filters are pretty hardy.

The cheapest route at the moment, would be to clean the MAF and the throttle body. If it clears up, but returns, replace the MAF.

I replaced my AOS b4 any symptoms such as lots and lots of smoke appeared. Cleaned the throttle body and the MAF at the same time as well. Had no error codes to speak of, but the RPM bounce went away.

You can DIY the MAF/Throttle Body/AOD yourself, but I would let the mech. do the Fuel Pump as it is located in the fuel tank.

According to some info I have, a fuel pump will fail earlier if the fuel tank is ran too many times at a low level.

No, there is no smoke on start up. But the exhaust smells of gasoline on start up and goes away after it warms up. Could possibly be the fuel pump, but what is the definition of "ran too many times at low level"? Below half? 1/4? To be honest I usually don't add my tank to full when i'm at the station.

[zodman]

Below 1/4 tank...near the range when the add fuel light comes on. Fuel pump tends to burn out if the fuel level is too low. To my knowledge when the fuel pump goes...it's gone. It doesn't "hang-in-there" for a while. Only a pending fault code could show beforehand.

Fuel smell in the exhaust just an educated guess, but I would think that the MAF maybe failing or is dirty. Reason being that the MAF isn't sending the proper sigs. to measure the air/fuel mixture. Hence...extra fuel blowing past.

Cheap DIY test to buy a can of MAF cleaner and clean the MAF. Long as your in there, check the air filter and clean the inside of the throttle body with TB cleaner. Check the j-tube (or Y-tube if so equipped) for oil residue too.

Do a search here for the MAF and the throttle body DIY instrux.

And of course, as Loren recommends, do a fault code readout and check for pending faults.

If you do buy a MAF, buy it at Sunset Imports not on e-bay...some peeps have been known to resell the used ones.

Edited November 25, 2009 by zodman

[Rui725]

I was just on the phone with the mechanic and he menitoned that there are some pending fault codes but they were "too messy" to pinpoint a problem?

No CEL.

He's testing the MAF now, I'm thinking to just changing it. The car is over 10 years old and still using the same original MAF. Its going to be replaced sooner or later.

[Rui725]

ok, results

MAF fine, fuel pump fine.

a set of O2 sensors completely dead.

does this sensor play a part in the rough start ups and gasoline smell in exhaust on cold start?

I haven't seen any of this sort. MAF maybe, but not O2?

[Loren]

Have cleaned the throttle body and Idle Control Valve?

AND... even thought you have no CEL - you should have the fault codes read. Look for pending faults.

[GTA_G20]

My 97 is the exact same but I was gonna swap motor regardless

No, there is no smoke on start up. But the exhaust smells of gasoline on start up and goes away after it warms up. Could possibly be the fuel pump, but what is the definition of "ran too many times at low level"? Below half? 1/4? To be honest I usually don't add my tank to full when i'm at the station.

Edited November 25, 2009 by GTA_G20

[Rui725]

Have cleaned the throttle body and Idle Control Valve?

AND... even thought you have no CEL - you should have the fault codes read. Look for pending faults.

The pending faults pointed to the 02 sensors.

I should've asked to have the throttle body cleaned, if i knew how to say it in mandarin! will have to look at the faq for that sometime

[Loren]

Have cleaned the throttle body and Idle Control Valve?

AND... even thought you have no CEL - you should have the fault codes read. Look for pending faults.

The pending faults pointed to the 02 sensors.

I should've asked to have the throttle body cleaned, if i knew how to say it in mandarin! will have to look at the faq for that sometime

Sorry, O2 sensors are after the fact - what are the pending fault codes?

[Rui725]

Have cleaned the throttle body and Idle Control Valve?

AND... even thought you have no CEL - you should have the fault codes read. Look for pending faults.

The pending faults pointed to the 02 sensors.

I should've asked to have the throttle body cleaned, if i knew how to say it in mandarin! will have to look at the faq for that sometime

Sorry, O2 sensors are after the fact - what are the pending fault codes?

hmm, the mechanic didn't tell me. I'll have to ask him again.