TheSamba.com :: View topic - cold idle/warm start problem stumps my mechanic

Thu Sep 04, 2008 8:28 am

I thought I'd post a problem I'm having with my '87 Westy that has stumped the mechanic I've been using for over 10 years who I trust and respect. Any thoughts will be very appreciated!

Current Problem:

The van starts well but idles very rough for about 45-60 secs before smoothing out. Then, once the van is warm (runs great warm) it does not restart properly. i have to crank the engine with the accelerator to the floor to get the thing to very gradually catch and start to fire. It then runs very rough for about 20 secs. Then smooths out and runs great.

History and Attempted Fixes:

Several months ago the van started having this problem: While the cold start was good, the cold idle was very rough for about 60 secs. Then the idle would smooth out but go to 2800 rpms for about 3 mins. Then the idle would drop but vacillate from 1200-2800 rpms, going up and down for about 3-5 mins. Then this would all stop and the van would run great (though the idle was as bit high - 1100-1200rpms.)

My mechanic replaced the idle stabilization unit and the van ran the same. He put the old one back. then we replaced the ECU with a used one from a reputable guy. he was able to then fine tune so the 2800 rpm and vacillation probs stopped, but now can't solve the current cold idle/warm start probs.

Prior to all of this, last year it had a bit of a cold idle issue which he dealt with by enriching the mixture. This fixed the prob but left me with a slightly high idle (1100-1200) which I just lived with for 6-8 months before the 2800rpm thing began.

Okay, so there it is. All ideas greatly appreciated! Thanks! John

Thu Sep 04, 2008 10:15 am

Use the search feature and look for TPS ...sounds like the first thing I would check is the Throttle Position Switch...there is a lot of information here about it, also how fresh is your O2 sensor,also unplug your Idle Stabl. Valve and see how it reacts

Thu Sep 04, 2008 2:00 pm

Test fuel pressures, and especially leakdown. If it fails to hold pressure after shutoff, ascertain whether the leakage is at the fuel pump, pressure regulator, or individual injectors by clamping the feed hose, return hose, or hoses to injectors, respectively.

Your mechanic should know that fuel pressure is a fundamental check on these systems. If you haven't established that the fuel supply is right, then all other attempts to diagnose problems may well be futile. The ECU has no way of knowing if this is wrong; you have to verify that as a foundation for everything the rest of the system does.

Check the coolant temp sender (Temp2) against the resistance-to-temp tables in Bentley, or simply replace this cheap and failure-prone item. New or not, pay special attention to its harness connector; tweak the female pins in the blue plug, spray out with contact cleaner, and reconnect with some dielectric grease or vaseline stuffed in the pins. The resistance across this circuit is a critical value the ECU needs, and additional resistance or erratic connection there can cause some of the symptoms you describe. This is a very common problem.

Check and adjust the throttle switch at the idle position.

Thu Sep 04, 2008 7:23 pm

awesome responses. thanks so much for your help. my mechanic is on holiday for 2 weeks, but i'll give him the feedback. cheers, john

Thu Sep 04, 2008 7:34 pm

Temp II sensor. Wiggled out/toasted Vacuum hose.

If that don't do it, then have to dig deeper.
:idea:

Fri Sep 05, 2008 12:22 am

All great advice!

Some things I noticed in my fight to get my doka smogged were, and I suggest that your mechanic do them in the following order:

Replace one or both fuel filters. My doka actually exhibited problems such as yours and had to get towed because the fuel filter was clogged. There were still idle and warmup issues that were gradually ironed out, but this is the first step.

Replace ALL the vacuum lines, it is a $6 fix.

Replace Cap and spark wires. I think at this point you are still under $50 in parts.

Check all the resistances in the wiring harness, by disconnecting the ECU and running the checks as per Bentley.

Check throttle switches.

O2 sensor, replace it and the co-axial wiring leading to the ECU. I put a custom molex waterproof connector on mine - most critical signal to the ECU, imo:
http://www.thesamba.com/vw/forum/viewtopic.php?t=286423&highlight=

Redo the timing. This is tricky for mechanics as it involves the idle stabilizer, the idle adjusting screw (reset to middle position), and once it is checked, you have to go back and backcheck everything with a smog test. THEN you tune the CO to limits, and do the timing again. You will see how good your mechanic is if he does that.

Here are some more idle performance threads for your edification:
http://www.thesamba.com/vw/forum/viewtopic.php?t=297431&highlight=
http://www.thesamba.com/vw/forum/viewtopic.php?t=291015&highlight=
http://www.thesamba.com/vw/forum/viewtopic.php?t=288260&highlight=
http://www.thesamba.com/vw/forum/viewtopic.php?t=276466&highlight=

Sun Sep 21, 2008 12:26 pm

Followed advice best I could by replacing suggested parts one by one. Wouldn't you know it was the cheapest of them all, the Temp II sensor. Fixed both the cold idle and warm start probs. You guys rule!

Mon Sep 22, 2008 5:52 am

I'm glad it was a simple solution. Thanks for letting us know what happened - it benefits all of us when people write back with results!