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View Full Version : Engine problems...won't start sometimes, dropping rpms



joeya103
01-09-2010, 01:08 PM
Hey all,

I tried to start my car the other night (temperature was in the 20s), and it wouldn't go. Then, I got a jump and it started up. On my way home, I noticed that whenever I was at a standstill, not pushing on the gas, the rpms would keep going up and down (normally idles at around 800...kept going from 400-800, shuddering, like it was about to shut off).

I replaced the battery and immediately tested it, and it worked. So I thought the problem was fixed. But just tried it again and it won't start again.

Is it the starter? I read something about solenoid or something. Plugs are relatively new...coil pack? ICM? I'm clueless. Please help guys!

jrodmk2
01-09-2010, 01:10 PM
i think there is a cold start sensor...or am i thinking of the vw side of things. will try and find it in the bently.

dangerous_dave
01-09-2010, 02:28 PM
Since you didn't tell us what kind of motor you have I will assume you have a 1.8t. But then again, you say you have an ignition control module so do you have a 12v V6? Next time you need help, please give as much vehicle identification as possible.

First thing I would do is clean the throttle body and do a throttle body alignment. If that didn't work I would look at fuel trim value block 32 on vag com. The trim percentages should be as close to zero as possible. If they are not close to zero, look for vacuum leaks and check how well your maf is flowing on value block 1 or 3, I forget which one it is. It should be above 2.5 gs. Preferably around 3-3.5 gs.

It could also be an idle control valve but since you didn't say what motor you have I don't know.

joeya103
01-09-2010, 11:10 PM
Thanks for the help, interesting possibilities.

BTW, you can see my engine near my avatar (1.8T). I thought it was clear there, sorry.

Mike@PureMS
01-10-2010, 07:36 AM
Since the battery was disconnected, you need to do a throttle body adaption.
Leave the key in the accessory position for 2 minutes without starting the car.

jpcallmotor
01-10-2010, 04:33 PM
Is everything back to normal? I am really thinking the alternator is toast. All the syptoms are there for a bad alternator. Do a few tests. Check voltage while car is running. Pull the B+ terminal off the pos. battery post. If the car dies, you need a new alternator. My VR6 Jetta is doing everything you mentioned in the first post.

walky_talky20
01-10-2010, 05:49 PM
joeya103: Is it cranking but not firing? Or not cranking at all? You have to be more specific than "it won't start". If it is cranking fine, but won't start it may be the Coolant Temp Sensor. If the alternator was bad I think you would see the Charging system warning while driving. Have you checked for codes?