Starts, runs 30 sec, idles very rough and dies

Post here for mechanical and engine topics such as fuel issues, transmission problems, rough idle, exhaust, electrical issues, etc

Moderators: GRNSHRK, ron, bfons

Post Reply
ReluctantRed
Posts: 14
Joined: Fri Oct 19, 2018 9:11 pm
Location: St. Louis USA

Starts, runs 30 sec, idles very rough and dies

Post by ReluctantRed »

New injectors have my 1987 635CSI running ok over 1000rpm. However idle is rough and gets progressive rougher as it runs for 30 to 50 seconds. After 50 seconds of running it won't idle, just dies. This is the "pasture" find I've been working on for several months, this car sat for 4-6 years, had bad gas, we have flushed a few times.

The idle air control motor appears to be new. Is it suppose to clank when you shake it like the later ones? On these cars, is the idle air control motor a stepper motor, or a DC motor? Its there a way to test it electrically? It only has 3 wires... +12, retract, extend. Can I just ground the extend wire to make it move?

We replaced the idle air motor's hose and the flex snorkel so there are no major air leaks.

The air flow door has me very confused. The whole resistor, pin 6 to pin 9 measures 562 ohms. The wiper (pin 7) measures 45 ohms to pin 6 when the door is closed. As you open it, the resistance goes up quickly to 850 ohms then drops to ~300 ohms and then increases to 560 ohms when its fully open. Is it suppose to work like this? I can't see how the wiper can have more resistance than the whole resistor unless there is a pile of dirt at one spot.

I don't think it has anything to do with O2, it never gets warm enough. Its only 4C outside here.

Cheers,
User avatar
86_6series
Platinum Member
Platinum Member
Posts: 1069
Joined: Mon Apr 02, 2007 10:08 pm
Location: West Nyack, NY

Re: Starts, runs 30 sec, idles very rough and dies

Post by 86_6series »

This should be some help in diagnosing your problem.

http://www.hiperformancestore.com/motronic.htm
86-635CSi
96-MB C220 SOLD
98-740i
71-Continental MK3
ReluctantRed
Posts: 14
Joined: Fri Oct 19, 2018 9:11 pm
Location: St. Louis USA

Re: Starts, runs 30 sec, idles very rough and dies

Post by ReluctantRed »

Has anyone removed the 7th injector? It look impossible to get at.

Its still original and it occurred to me if its leaking, it would idle ok when it first starts and needs gas but would be too rich as it ran for a while which is exactly what it doing.

Thanks for the link to the Motronic write up. I've read it before but its packed with information and need to be read over and over.
User avatar
tschultz
Posts: 2515
Joined: Wed Jul 07, 2010 10:54 pm
Location: Colorado
Contact:

Re: Starts, runs 30 sec, idles very rough and dies

Post by tschultz »

You could remove for plug the fuel line to that cold start injector if needed...
http://www.Drive4Corners.com
Image
'79 635CSi Revival
'80 635CSi
'83 633CSi Callaway Turbo continued as 1988 535is Turbo
SOLD: '81 635CSi/A
User avatar
86_6series
Platinum Member
Platinum Member
Posts: 1069
Joined: Mon Apr 02, 2007 10:08 pm
Location: West Nyack, NY

Re: Starts, runs 30 sec, idles very rough and dies

Post by 86_6series »

ReluctantRed wrote: Wed Nov 21, 2018 12:39 pm Has anyone removed the 7th injector? It look impossible to get at.

Its still original and it occurred to me if its leaking, it would idle ok when it first starts and needs gas but would be too rich as it ran for a while which is exactly what it doing.
Yes, very difficult to get that out. IIRC I chiseled it to make room to
remove the bolts. Then, installed the new one with allen head bolts.
86-635CSi
96-MB C220 SOLD
98-740i
71-Continental MK3
ReluctantRed
Posts: 14
Joined: Fri Oct 19, 2018 9:11 pm
Location: St. Louis USA

Re: Starts, runs 30 sec, idles very rough and dies

Post by ReluctantRed »

That a good suggestion to block the hose. I'll try that next.

The idle control motor was not moving, cleaned it, works good now, can hear it clacking on the engine now, but she still dies at idle.
User avatar
slofut
Posts: 778
Joined: Thu May 30, 2013 1:29 am
Location: SW Ga

Re: Starts, runs 30 sec, idles very rough and dies

Post by slofut »

Possible it is running only on the cold start injector (unplug csi and it won't fire off at all). Main injectors not firing etc... check crank sensor for pulsing with ohm meter (ecm uses this signal to fire injectors) and voltage at injectors when cranking and or running. Ecm breaks ground on the injectors iirc.
'87 635csi, 5sp man, dk blu on pearl beige
'88 635csi, auto, black on grey
'63 BMW Isetta
'75 XJ6C, 2dr, warm 350
'86 XJ6, th700r4
'75TR6
'64 Olds 88 conv
"68 T120 Bonneville
Post Reply