Author Topic: idle misses/surges with no check engine light (Read 3898 times)

bim(noob)mer · « **on:** August 28, 2011, 11:29:59 PM »

As the title states I have a 1991 318i and the idle will sometime jump or surge even while driving. I have already searched this forum as well as r3vlimited and e30tech and bimmerworld. I checked the harness without taking the upper manifold off because the gasket between upper and lower is in the mail.

I do NOT get a check engine light but the car seems to misfire or surge completely randomly. It's almost as though I have a tank of bad gas but I have refilled the tank several times and even added fuel injector cleaner and get the same result. The strange thing is some times I can go a whole day without it ever surging at idle or misfiring while driving.:confused: This is very annoying as the car runs perfectly and gets awesome gas mileage besides this. Any info/help would be awesome.

bim(noob)mer · « **Reply #1 on:** August 29, 2011, 03:25:01 PM »

DesktopDave · « **Reply #2 on:** August 29, 2011, 04:49:47 PM »

Might be a vac leak or an ICV issue. Have you considered the hose delete mod? There are a LOT of hoses and they tend to decay over the years.

The '91 won't light the CEL unless you have an O2 sensor issue. It's not a very advanced system. Try the "stomp test" instead...let us know what it tells you. I'm betting a 1221 O2 code from vac leaks.

Other possible causes...coils, coil wires, crank or cam position sensor, fuel pump, the list goes on and on.

bim(noob)mer · « **Reply #3 on:** August 29, 2011, 11:22:06 PM »

Yeah the PO said he replaced all those "under intake mess" hoses with the oem ones. I actually found his post about it on here lol. Anyways I have a box of stuff in the mail with various gaskets and a fuel filter that I am planing on using whenever fedex decides to show up. I will def do the "stomp test" wed while I'm putting on all the goods. Thanks for the response.

bim(noob)mer · « **Reply #4 on:** August 29, 2011, 11:24:56 PM »

oh and just to add the wires are those aftermarket individual ground "honda ricer" plug wires so I will probably be checking those as well. I have read some people's stories about those just crapping out.

DesktopDave · « **Reply #5 on:** August 30, 2011, 07:26:11 AM »

Give that crank position sensor a good cleaning too. It's difficult to remove as the A/C bracket has to come off, but just cleaning up oil & rust off the sensor's flat metal face and making sure it's really close to the crank trigger wheel are important. That crank sensor is critical...and the car won't run without that sensor working.

I'd also whip out my trusty multi-meter and get a resistance reading off the CPS plug under the intake manifold. Should be around 500 or 600 ohms.

I'm not sure about the wires...apparently there is a cross-ref for Hyundai plug wires that fit our cars...but it's good to get a resistance reading off them too.

bim(noob)mer · « **Reply #6 on:** August 31, 2011, 07:26:07 PM »

Ok, so today I had a little time to spend under the hood and did the "stomp test". I luckily only received one code, 1234, I looked this up but could not find a translation for it. I did two or three "stomp tests" but I got the same code and it repeated over and over again. I found the code on an e38 dme fault code list but none on e30.

bim(noob)mer · « **Reply #7 on:** August 31, 2011, 07:52:22 PM »

I found an e30 fault code description for 1234 but it was for vehicle speed sensor(speedometer signal A). The weird thing about that is my speedo works and I have checked this with a drive by radar trap.

?

DesktopDave · « **Reply #8 on:** August 31, 2011, 08:45:11 PM »

Well, that's a start. With any Motronic code, the next step is to determine if it's the sensor that's at fault, or if the system is generating phantom codes. I usually try to mystically channel a German engineer.

I'm guessing that the speedo does send a signal to the computer (DME). I'm further guessing that I'd measure "load" that way (if I was a German engineer).

The speedo isn't the trouble. It might be the gauge cluster distribution board or a loose terminal from the sender. Let me see if I can find the wire that you should be testing.

From the e30 Electrical Troubleshooting Manual, it looks like the cluster definitely sends a signal from connector C2 pin 10 (Blue/Yellow) to the C101 connector pin 14 (round chassis connector on the firewall), where it connects to a Black/White wire and finally gets to the DME on pin 29. Check that wire for continuity from the C101 to the DME. Ist dass unser problem?

Sorry, forgot to channel back...I'd also be tempted to dab a bit of dielectric grease on those pins in C101.

bim(noob)mer · « **Reply #9 on:** September 06, 2011, 09:56:07 PM »

Sorry I haven't gotten on here for updates. I tested some various connections and the resistance readings all seemed to be in spec per the haynes and info online. I did notice some cracks forming on the line around the "mess under the intake". I am saving/compiling stuff for that mod, I plan on 4 pintle mustang injectors cleaned and balanced by RC and doing the heater plate removal and 3 hose/line mod under the intake. Also, I am planning on replacing the fpr while I'm in there, and the coolant pipe thing with proper o-ring. On a side note today I fixed my oil leak today. I couldn't find it until 1 day last week I shut the car off and looked in between the timing chain cover and the pulley teeth on the front of the engine driver's side and noticed a trickle of oil running down there. It ended up being the oil filter housing to block gasket and corresponding o-ring. I replaced them today and the car already feels better and the piece of mind is awesome. Whew that was long winded.