Sometimes: rough starting, then all is fine?

[MichailS]

Hello

Recently when I have started my PAU -94 it has coughed a lot initially but after a few seconds all is well. I turn the key, the engine starts right away, it blubbers and mutters and coughs a bit, then it settles on a nice regular idle within 5-10 seconds. It runs smooth in operation.

This doesn't happen all the time, I am not sure about the pattern but it seems to only happen when the engine is cold. For a while it seemed as strong summer sun was related as well, since it doesn't seem to happen as much on colder mornings. I could be making erroneous connections here though.

What could it be? Oxygen sensor? Supercharger idling valve? Dirty throttle?

[Alibi]

How about a good cleaning? http://www.lesabret.com/phpBB/viewtopic.php?t=4054

I'd say your IAC valve just needs a good scrubbing. Is the SES light on?

[wrightz28]

Intake air temp sensors (normally located in the air filter housing) are known to cause this behvior when they get dirty/go bad/ or have wiring issues.

[MichailS]

Wow, thanks! I had no idea it would be that simple!

I'll try it tomorrow.

[auto trainy]

Just a quick question,have you been using any antifreeze?

[Alibi]

Originally Posted by auto trainy

Just a quick question,have you been using any antifreeze?

For his sake I hope he isn't.

As for the air temp sensor, it ought to throw a code, but if I remember right from the one that went bad on mine that it didn't trip the SES light, but was only stored in the ECM's memory. Either way, I'd suggest that you clean (almost free) before you start replacing parts, although I doubt that sensor is any more than $10-15.

[MichailS]

Originally Posted by auto trainy

Just a quick question,have you been using any antifreeze?

You mean antifreeze as in coolant liquid, or antifreeze as in that gas that people spray in the intake on cold mornings? Yay to the former, nay to the latter.

[Alibi]

"using" as in has the level of antifreeze been slowly draining lower, but without any visible leaks or puddles on the ground. Worst case scenario would be that you have a head gasket leak, but that wasn't nearly as common on the series I engines as they still had an aluminum intake manifold. The later series II had a plastic manifold that would warp/melt around an EGR pipe, causing a leak.

[auto trainy]

If it was my car ,I would have the cooling system pressure tested just to be sure,good luck and let us know how you make out.

[Bassasasin]

I want to try to help.. here goes.

RUN mode: (Just trying starting) First crank.
Good to take note that the engine begins starts on sensor samples of (ECT) Engine Temperature Sensor {checking for a cold start} and (TP) Throttle Position sensor.

Then (over 400rpm) its running in a OPEN LOOP mode which ignores sensors like O2 sensor and uses sensors TP, ECT and MAF (Mass Air Flow).

AND Note that these are stored to your personal engine in the PROM in the PCM computer for probable future starts.

If the engine starts like you say it sounds like its starting LEAN right away. Try having someone look during the cold start at the exhaust for either black smoke puff or barely any smoke or none.
Rich fuel = black, lean = clear or a worse condition if WHITE = coolant head gasket leak.(bad$$$)

RUN Possibilities (under 400rpm) are: Either the TP, or the ECT sensor is bad or your PCM is starting with the wrong settings for the mixture for a good start or Fuel pump may also not be sending enough pressure for its start inject pulse or because of the PCM or the fuel pump itself isnt sending the pulse.
OVER 400rpm Suspect the MAF sensor.

Try disconnecting the battery for 30 seconds or more to reset the PCM.
See if it starts better for a while like about 10 starts.

After everything is up and good the O2 sensor heats up and the engine goes into a Closed Loop run.

I noted you said occasionally... well that injects the TPS as prime suspect. It can get dirty on the electric wipers.. since the MAF sensor is goobered all the time when its dirty. The ECT is usually bad all the time when bad.. .. Just thoughts.
Also all electric connections are assumed to be good.


GOOD LUCK..

[MichailS]

I have seen no smoke and the coolant level is good. This is the supercharged engine so it doesn't have the melting plastic manifold.

First thing I shall do is change the gas filter, because last time I had it at the shop they said it had been running somewhat lean. Have one waiting in the trunk since months...

Then I'll clean the intake stuff and hope that'll be it. If not, I'll go further in my investigations. Or simply leave it to the shop, which I want to avoid since they are far away. =/

Thanks a million for all your kind help!

[Bassasasin]

Its important to note the RPM speed of 400.. things change after that.
Fuel filter usually causes poor power under load conditions, uphill at high speed etc. sinnce its clogged all the time basically but a good place to look. Lots of bad gas has been circulating around the pumps lately.
Hope you do the battery disconnect first before the $$ are passed out.

Other things may be EGR valve stuck open, Ocasionally.

Bass...