I have searched all over trying to find a potential cause for this issue and thus far I haven't found one. The most common issues I have read about aren't quite like this one.
3/1987 325is, 5 speed. Not sure which motronic it is, the car has ABS but doesn't store codes.
I'll start with a video demonstrating it:
http://www.youtube.com/watch?v=vQp_fGGTqVM
Ignore the whining, that's just my trans bearings failing.
The issue is not the idle when cold, but rather when giving the car gas off-idle. It sputters and almost dies, revs to about 1500 and then settles back down if you give it a press on the throttle, such as you would do when starting from a stop, which has made driving it while cold (even gently) nearly impossible to do without revving it to 2k or so rpm and slipping the clutch like crazy to get it to not stall. The issue *almost* completely disappears when the engine is at operating temp.
I started by checking for vacuum leaks, and I couldn't find any. I swapped the head with a rebuilt one in August which of course meant all new intake seals, torqued to spec, etc. Every vacuum line (brake booster, evap, PCV, etc) is new with new OEM BMW clamps, and I have confirmed that the intake boot has no cracks or holes in it.
The next thing I tested were all the sensors that had to do with cold operation. I started with coolant temp sensor (blue plug) which I had thought was the culprit since it seems like a common failure point. It read 2600 ohms at room temp (car had been sitting for 4 days, garage was ~65 degrees) and when I started the car and let it idle, that number steadily dwindled, like it is supposed to. I did not check it at operating temp, but that is not where my issues are. I will move the car outside tonight (supposed to be 15 degrees) and see if it reads more ohms when real cold.
I then tested the TPS, it was correct. Clicks when throttle is moved just off idle, and left / middle pins lose continuity when they should, and right / middle pins get continuity a little before WOT, all the way to WOT. So TPS is okay. I then took the airbox out and tested the intake air temp sensor, which read 3600 ohms at room temp (I think this was a little high but the metal felt colder than 65 degrees). I opened the air meter door and shot hot air in it with a heat gun, and the lowest the ohms would get was 1100, I think it is supposed to get lower than this at that kind of heat, but it did quickly respond to the heat. I then tested the air meter with an ohmmeter (one site said you can't test it like this, is that true?) and the ohms steadily decreased as the door was opened, with no dead spots that I could tell. I have not yet attempted to open it and move the contacts yet.
The last injection computer related thing I tested was the IAV. With it plugged in and ignition on, it buzzes. I tested it with an ohmmeter to some specs I found that I THINK were for this IAV (the larger metal 90 degree one), something like 20 homs between two pins and then 40 ohms between another. I tested voltage at the plug, and got 9.6 at one and ~3.6 at the other. When manually opened, the valve closes all the way when plugged into the car and the ignition turned on, and does not fall back open when power is removed. There is little if any discernible change in engine speed or behavior when the IAV is unplugged and the engine is running.
The last thing I checked last night was fuel pressure. I didn't have a real fuel pressure gauge, but I was curious so I took the air pressure gauge off a shitty craftsman compressor, hose clamped it to a short section of hose and tee fitting, and put the tee fitting between the fuel supply to the fuel rail and started the motor. Now I don't know if an air pressure gauge works for liquid pressure, or if that gauge is accurate at all, but it only read 10 psi at idle, and 12 psi with the vacuum line to the FPR removed, spec is 40-45 at idle and higher with that vac line removed. I will test again tonight with a real fuel pressure gauge. Would the car even run with that little fuel pressure? Side note: when I pulled the fuel supply line to the FPR, it was BONE DRY. Not a drop of fuel came out. Fuel isn't supposed to drain back past the pump, is it? The car was sitting for ~4 days before I cracked it. It has had no issues starting.
One last dumbass thing I should check is to make sure I didn't put the fuel lines on backwards when I put the engine back together after the head swap...would it even run if those lines were reversed?
I appreciate any help or advice.
-JB
3/1987 325is, 5 speed. Not sure which motronic it is, the car has ABS but doesn't store codes.
I'll start with a video demonstrating it:
http://www.youtube.com/watch?v=vQp_fGGTqVM
Ignore the whining, that's just my trans bearings failing.
The issue is not the idle when cold, but rather when giving the car gas off-idle. It sputters and almost dies, revs to about 1500 and then settles back down if you give it a press on the throttle, such as you would do when starting from a stop, which has made driving it while cold (even gently) nearly impossible to do without revving it to 2k or so rpm and slipping the clutch like crazy to get it to not stall. The issue *almost* completely disappears when the engine is at operating temp.
I started by checking for vacuum leaks, and I couldn't find any. I swapped the head with a rebuilt one in August which of course meant all new intake seals, torqued to spec, etc. Every vacuum line (brake booster, evap, PCV, etc) is new with new OEM BMW clamps, and I have confirmed that the intake boot has no cracks or holes in it.
The next thing I tested were all the sensors that had to do with cold operation. I started with coolant temp sensor (blue plug) which I had thought was the culprit since it seems like a common failure point. It read 2600 ohms at room temp (car had been sitting for 4 days, garage was ~65 degrees) and when I started the car and let it idle, that number steadily dwindled, like it is supposed to. I did not check it at operating temp, but that is not where my issues are. I will move the car outside tonight (supposed to be 15 degrees) and see if it reads more ohms when real cold.
I then tested the TPS, it was correct. Clicks when throttle is moved just off idle, and left / middle pins lose continuity when they should, and right / middle pins get continuity a little before WOT, all the way to WOT. So TPS is okay. I then took the airbox out and tested the intake air temp sensor, which read 3600 ohms at room temp (I think this was a little high but the metal felt colder than 65 degrees). I opened the air meter door and shot hot air in it with a heat gun, and the lowest the ohms would get was 1100, I think it is supposed to get lower than this at that kind of heat, but it did quickly respond to the heat. I then tested the air meter with an ohmmeter (one site said you can't test it like this, is that true?) and the ohms steadily decreased as the door was opened, with no dead spots that I could tell. I have not yet attempted to open it and move the contacts yet.
The last injection computer related thing I tested was the IAV. With it plugged in and ignition on, it buzzes. I tested it with an ohmmeter to some specs I found that I THINK were for this IAV (the larger metal 90 degree one), something like 20 homs between two pins and then 40 ohms between another. I tested voltage at the plug, and got 9.6 at one and ~3.6 at the other. When manually opened, the valve closes all the way when plugged into the car and the ignition turned on, and does not fall back open when power is removed. There is little if any discernible change in engine speed or behavior when the IAV is unplugged and the engine is running.
The last thing I checked last night was fuel pressure. I didn't have a real fuel pressure gauge, but I was curious so I took the air pressure gauge off a shitty craftsman compressor, hose clamped it to a short section of hose and tee fitting, and put the tee fitting between the fuel supply to the fuel rail and started the motor. Now I don't know if an air pressure gauge works for liquid pressure, or if that gauge is accurate at all, but it only read 10 psi at idle, and 12 psi with the vacuum line to the FPR removed, spec is 40-45 at idle and higher with that vac line removed. I will test again tonight with a real fuel pressure gauge. Would the car even run with that little fuel pressure? Side note: when I pulled the fuel supply line to the FPR, it was BONE DRY. Not a drop of fuel came out. Fuel isn't supposed to drain back past the pump, is it? The car was sitting for ~4 days before I cracked it. It has had no issues starting.
One last dumbass thing I should check is to make sure I didn't put the fuel lines on backwards when I put the engine back together after the head swap...would it even run if those lines were reversed?
I appreciate any help or advice.
-JB
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