surging problem 5 to 10 min after warmup

[Vincenzo533i louisville]

well I have a problem with my 84 533i. it starts fine but about 5 to 10 min after it reaches operating temperature it has an extreamly eratic idle. even when it is in gear the engine surges so much that the whole car bucks like no other and it keeps getting worse till you try to pull away and the engine just dies. now I have tested the coil, tryed a new ECU, wires cap and roater are almost brand new only about 1 to 2 thousand miles on em. I also just replaced the crankshaft position sensor, speed sensor and o2 sensor when I did the head rebuild. I have apsolutly no clue what it is and I would love some feedback so I can get this bimmer back where it belongs, on the road with me driving it. thanks

[pdx 528e]

Just to remove doubt, have you checked for vacuum leaks? In what condition is your fuel system, injectors, FPR? Sounds like it is lean surging.. but im not sure why it does only when it gets to operating temperature. Mine does it when dead cold, but never once warm.

[Mark 88/M5 Houston]

If I understand your post, this is an idle problem. The 533i ECU does not control the idle. There is another small box (generally green or black) mounted with the ECU that is the idle control module. May also be a bad idle control valve. You mentioned doing the head - did you reuse all your old hoses and intake bits or did you replace all that. You should also clean the connector on the AFM and insure that your TPS is clean and adjusted properly.

AFM = Air flow meter
TPS = Throttle position sensor/switch

[Mike in Louisville]

The problem isn't just the idle (I rode in the car today). It runs well until a couple minutes of operating temperature, and then it craps out. Pulling away, in first or second, the car hesitates and then pulls and often bucks again. This is not just the bottom of the RPM, but all the way through. At constant speed it is the same thing. Eventually, the car dies and will not start. It still has spark and fuel however when it dies. I agree that the AFM and TPS might be the problem. Does anybody know if the coolant temp sensor could cause this? The temp gauge went out and a ricer-looking VDO one was added, just tapping into the wires for the original one. However, this was done awhile ago and didn't affect engine operation at the time. Vacuum leaks, too, wow this is a lot of fun to troubleshoot %) I guess it wouldn't really be a hobby if there wasn't any work involved.

[pdx 528e]

[QUOTE="Mike in Louisville"]Does anybody know if the coolant temp sensor could cause this? [/QUOTE]

Bentley suggests testing coolant temperature sensors in the multitude of troubleshooting hints provided for "warm idle troubleshooting" on chapter 3, page 17.

[bobby in Derby City]

Hey Mike, you found a new recruit in tha Derby City. You are right about us needing to have a wrenchfest sometime. Will holla back

[M3 Ryan]

My '87 535 drove me NUTS with a problem like this last year. It lasted 6 months until finally the ECU took a crap. I swaped it out and havn't had a problem since.
I replaced main/fuel pump relays, intake boot, and a few other small bits but nothing made a differnece until finally the ecu gave up and the car wouldn't start. might not be the same problem on your 533 but it is a possibility.

[Vincenzo533i louisville]

yeah well I have already tried replaceing the ECU and when I put the new one in it did the exact same thing once I started it up. I am really boggled by this. I don't have any vacume leaks eather, cause that could do it. the coil is good and cap and roater are new. both the cranshaft position sensor and speed sensor have been replaced. and the wierd thing is when the car has been sitting for a long period of time it will start up and run fine till a couple of mins after warm up. but it is getting worse and worse. I used to be able to just let it cool for ten min or so but not anymore. now I have to wait like an hour or so before it will even start again. it doesn't make any sense at all. anyway thats for all your sugestions and if you got any more pass them along. cause there is no way on earth I am getting rid of this car.

[Guest]

Does anybody know if the coolant temp sensor could cause this? The temp gauge went out and a ricer-looking VDO one was added, just tapping into the wires for the original one.

I believe you might have identified the problem area. There was a service bulletin on the 533i which added a small precision resistor in the Coolant Temp Sensor line., I don't recall the exact value, something like 470 ohms. The resistor is hidden under the boot for the connector on the Coolant Temp Sensor and it is easily broken.

This is the first thing I would check, followed by the CTS itself.

Rich

[fastpat]

[QUOTE="Vincenzo533i louisville"]well I have a problem with my 84 533i. it starts fine but about 5 to 10 min after it reaches operating temperature it has an extreamly eratic idle. even when it is in gear the engine surges so much that the whole car bucks like no other and it keeps getting worse till you try to pull away and the engine just dies. now I have tested the coil, tryed a new ECU, wires cap and roater are almost brand new only about 1 to 2 thousand miles on em. I also just replaced the crankshaft position sensor, speed sensor and o2 sensor when I did the head rebuild. I have apsolutly no clue what it is and I would love some feedback so I can get this bimmer back where it belongs, on the road with me driving it. thanks[/QUOTE]

Looks like your problems begin after the cold start system shuts off completely. I'd try putting a fuel pressure gauge on the fuel system and find out if you have the correct 3.0 bar pressure.

[Vincenzo533i louisville]

hey guys well I found the problem. it ended up being the Idle control valve. Which was one of the first conponents that I tested but since at first it was an intermitant problem It tested out good. anyway I got one and it runs pritty good now. thanks for all your input and Ideas.