wont start when warmed up, why? on 1993 Volkswagen EuroVan

This eurovan has automatic trans. all systems seem to work ok. when first started. starts easy, idles fast for couple minutes, the drives normal. after driving for least 20 min, it may or may not stall when stopped, at this point it will turn over well, but not restart. been towed twice, starts easy after sitting for a couple hours or overnight. no check eng. lite, dont think it has one. Done major tune up, new battery, o2 sensor and catalytic converter. where should I be looking for problem? Im starting to think the ecu or idle control valve.

by in San Jose, CA on February 08, 2014
1 answer 9 comments
ANSWER by on February 08, 2014
An idle valve will not keep a car from starting. It controls air, not fuel or spark. ECU is very rare to cause an intermittent no start. You need to see if your no start is from lack of spark or fuel. Do you know how to do this? Do you have a test light? I would check for power on the coil with key on and then cranking. When not cranking, both sides of the primary side of the coil should be hot. when cranking, one side should stay hot and the other should pulse or blink. If both sides stay "hot" and don't blink, I would suspect a bad Hall sensor in the distributor...see http://www.youtube.com/watch?v=jJmqdhhduVc
COMMENT by on February 08, 2014
Thanks Ill try testing coil, I have test lite and will follow your directions and reply again when done. OK I tried testing coil, I have 3 wires going into coil, blk, green, brown, Key on, power only at blk lead, Green shows nothing, brown goes to ground. when starting, blk pulses, green does nothing and brown is ground. Started ok and idled for 10 minutes with no problem, then suddenly idle dropped to zero, motor stopped, bur restarted easily,i raised rpm to 2500 and released, idle went to zero again. restarted ok again and idle held by self at 750 rpm with no further problems even after raising idle a few times, after 35 min I shut off. Note: relays by radiator in front of battery got very warm, these relays are 86 86 114 111 and 111. I have no idea what they do or if they are affected by heat, do you? I think im ready to try something else, thanks bob
COMMENT by on February 09, 2014
Relays do cause a lot of problems...Tap on them with a back of a screwdriver when it is running. Also check for loose grounds. You may grab the car's wiring harness and wiggle it to see if it dies.
COMMENT by on February 09, 2014
Thanks, took your advise, checked all relays I could find, by tapping when warm, no effect, I then wiggled any and all wiring I could find, no effect. I then looked for and wiggled all ground wires I could find, no effect. I wonder if maybe its a fuel problem, I don't know how to check for that. I will try whatever you suggest, This is a real tough one. Thanks for your help. Bob
COMMENT by on February 09, 2014
You are going to need a fuel pressure gauge....A high pressure one. Can you get one?
COMMENT by on February 09, 2014
Yes I can, would you know the Brand and type needed? Do you think it possible some other elect. or sensor or gauge could be involved? Or what we can eliminate for sure. Is there a test for the Hall sensor?
COMMENT by on February 09, 2014
When it dies take the coil wire out of the center of the distributor and check for spark. Have to see if you are losing fuel or spark
COMMENT by on February 09, 2014
Sounds like a good place to start, I will work on that, except I never know when its going to die, also do I hold the wire from the dist. to or near ground ? will I get shocked? Should I get the fuel pressure gauge ready? I really will have to buy you a drink after this is over. thanks again
COMMENT by on February 10, 2014
Invest in a spark tester so you don't get shocked http://www.amazon.com/OTC-6589-Electronic-Ignition-Tester/dp/B0050SFVO2/ref=sr_1_1?ie=UTF8&qid=1392040695&sr=8-1&keywords=spark+tester+automotive
COMMENT by on February 10, 2014
I cant believe it, but I fixed it. The MAIN problem was the ECU RELAY, replaced that and the starting problem was fixed...also replaced the fuel relay. The idle dying problem was due to a very dirty Air mas sensor inside of the dirty throttle body and valve. Runs great now. also replaced coil, plugs wires dist cap rotor all filters and fluids. .. Thanks for all the help That all helped, but the true problem was the Hall sensor in the distributor, it only quit when hot and will work great when cool. Its realy running great now. That was a lot of fun