choppy acceleration
- Thread starter imtjm
- Start date
On the earlly 318i's supposivly when the idle control valve goes it it causes the idle control module to burn out. I have read that if you need to replace one, replace them both. I have had two early 318i's and had problems with the idle control system.
FYI, the early 318i's DO NOT have a mass air flow sensor, they have a air flow meter just the the 325's.... and I am pretty sure its the same AFM. Hell I have two extra AFM's, one off a early 318i and one off a 325 and they look identical.
Another FYI, the 318i's ECU is real basic, it does not even control the ignition timing like the 325's. The ECU does not know when the A/C is on or off, it just controls the mixture and thats it. You cant even get a computer chip for the Jetronic ECU thats in the 318i's.
You can test the idel control valve and idle control module with an ohm meter. A bentley manual should say the OHM specs. It may be causing your problem but I kinda doubt it. You say this is a new a/c compressor? If you got a used one, I wonder if one of the bearings inside the unit is going out and causing your choppy acceleration.
Its good to finally be back on the internet. Later.
FYI, the early 318i's DO NOT have a mass air flow sensor, they have a air flow meter just the the 325's.... and I am pretty sure its the same AFM. Hell I have two extra AFM's, one off a early 318i and one off a 325 and they look identical.
Another FYI, the 318i's ECU is real basic, it does not even control the ignition timing like the 325's. The ECU does not know when the A/C is on or off, it just controls the mixture and thats it. You cant even get a computer chip for the Jetronic ECU thats in the 318i's.
You can test the idel control valve and idle control module with an ohm meter. A bentley manual should say the OHM specs. It may be causing your problem but I kinda doubt it. You say this is a new a/c compressor? If you got a used one, I wonder if one of the bearings inside the unit is going out and causing your choppy acceleration.
Its good to finally be back on the internet. Later.
if the early 318i does not have an air flow sensor, what are the pentoids (pentodes??) that have detachable wire (one going attaches to the air hose going into the AFM and one going into the AFM). If the little things (i guess they are called pentoids or whatever) sticking out of the hose and the AFM that attach to wires aren't sensors, then i don't know what you mean by sensor.
the ICV works and i've swapped it out before thinking it was a problem. i also swapped out the icu. bentley also says that even though the icu may test good, it may not be good (or maybe someone else said that). i haven't tested the ecu yet, so i'll do that.
i have a spare ECU i bought so i may just swap that out and see if things are better. if you say the ecu does not sense if the a/c is on, then i guess changing though out won't matter.
if the icu doesn't sense if the a/c is on, then it doesn't seem that either the icv or icu would be the problem, b/c i would have the same problem irregardless of whether the a/c was on or not.
there has to be something that senses that the a/c is on to make sure the car is getting enough air, gas, or whatever isn't there? i notice that when i turn the a/c on, the idle drops for a half second (which i figure is b/c of the extra electrical load) and then bumps back up (this is a change from earlier post where i stated that my idle decreases, it doesn't it stays normal, just for the first half second it drops then goes back up, but it still, or at least i can't tell, doesn't increase 100rpm as someone said).
maybe it is the throttle and with the extra load of the a/c it just amplifies it. it doesn't seem to be happening though without the a/c, but i'll be more attentive to see.
thanks all for the input.
the ICV works and i've swapped it out before thinking it was a problem. i also swapped out the icu. bentley also says that even though the icu may test good, it may not be good (or maybe someone else said that). i haven't tested the ecu yet, so i'll do that.
i have a spare ECU i bought so i may just swap that out and see if things are better. if you say the ecu does not sense if the a/c is on, then i guess changing though out won't matter.
if the icu doesn't sense if the a/c is on, then it doesn't seem that either the icv or icu would be the problem, b/c i would have the same problem irregardless of whether the a/c was on or not.
there has to be something that senses that the a/c is on to make sure the car is getting enough air, gas, or whatever isn't there? i notice that when i turn the a/c on, the idle drops for a half second (which i figure is b/c of the extra electrical load) and then bumps back up (this is a change from earlier post where i stated that my idle decreases, it doesn't it stays normal, just for the first half second it drops then goes back up, but it still, or at least i can't tell, doesn't increase 100rpm as someone said).
maybe it is the throttle and with the extra load of the a/c it just amplifies it. it doesn't seem to be happening though without the a/c, but i'll be more attentive to see.
thanks all for the input.
I think the A/c is driven by a belt and it does not put any electrical load on anything because it just doesn't use any electricity. I don't remember for sure but I think the same happens to my car, the idle drops just a bit and then rises, I just don't remember if it rises to where it was or 100rpm higher. Come to think of it, if it does drop and then does go up, the car somehow has to know that you just turned the A/C on otherwise it would just drop and stay there, like you engaged the clutch a little. The whole thing is really confusing. I personally have noticed choppy acceleration lately but that is because of the road I have been taking lately and it is the traction control taking over, thats nothing even close to you.
Maybe the problem is not even related to the ICU/ICV, I mean they should only control Idle rpm and not the whole rpm range at least if you go by the name. Try going somewhere with no cars and just do a couple of runs, accelerating from one speed to another with the A/C of and on and see what really happens. Hope you resolve this issue and good luck.
Maybe the problem is not even related to the ICU/ICV, I mean they should only control Idle rpm and not the whole rpm range at least if you go by the name. Try going somewhere with no cars and just do a couple of runs, accelerating from one speed to another with the A/C of and on and see what really happens. Hope you resolve this issue and good luck.
The Idle control system is designed to sense when the RPM's drop bellow a certain point, and then let the idle control valve to open slightly more to let a little more air in to compensate for the extra load of the A/C unit.
When I turned on the A/C in my 318i it also engaged the auxilary fan. So I figure that the compressor and the fan pulled about 30 horsepower, wich is a big chunk out of the factory 105 horsepower that the 318i produced. This 30 horsepower lowers the idle, so then the idle computer would senser this with its Tach lead and then let the idle valve open slightly more to compensate.
That little sensor inside the air inlet hose is to sense the incoming air tempurature, atleast thats what I was told. I cannot remember the proper name for it, it does have one. And I cannot remember right now what the little sensor inside the inlet of the AFM is. It is testable though, I have checked them before. I think it was like an o2 sensor but I may be wrong.
When I turned on the A/C in my 318i it also engaged the auxilary fan. So I figure that the compressor and the fan pulled about 30 horsepower, wich is a big chunk out of the factory 105 horsepower that the 318i produced. This 30 horsepower lowers the idle, so then the idle computer would senser this with its Tach lead and then let the idle valve open slightly more to compensate.
That little sensor inside the air inlet hose is to sense the incoming air tempurature, atleast thats what I was told. I cannot remember the proper name for it, it does have one. And I cannot remember right now what the little sensor inside the inlet of the AFM is. It is testable though, I have checked them before. I think it was like an o2 sensor but I may be wrong.
While the cars are technologically very different, I had this same problem with my '89 325i. Poor acceleration in the lower RPM's with A/C on. After changing the O2 sensor due to a problem with starting problem (Heater circuit in the sensor itself) the problem went away. Looks like more than just the heater circuit was damaged.
after i soldered the wire in the wire harness to the ICU, i discovered the O2 sensor wire was unplugged. when i connected it, i got choppy acceleration again. i removed the old O2 sensor and it was all clogged up, so i replaced it. acceleration was good for a day, then i got choppy acceleration again for some reason, so i've been messing round with the throttle position switch. now i have sporadic choppy acceleration. so the next thing will be to get a new throttle position switch. i'm not entirely convinced mine is bad though. i've followed bentley's testing of the throttle position switch (TPS), but i'm getting mixed results. slight actuation of the throttle produces continuity. i think it's failing the half way test though. is the TPS supposed to show a reading on the ohmometer when at rest? bentley sort of gives mixed. it states that you should adjust TPS so there is continuity (0 ohms), but in the testing portion of the paragraph it says the TPS should register continuity when throttle is slightly activated (.002-.006 from rest position). this suggests that at rest position the TPS should not have continuity, so there should be some reading on the ohmometer, which i get. anyone have any suggestions? i guess i'll end up replacing the TPS in the end. I've replaced lots of parts thus far that have not proven faulty or fixed the problems i've been having (high operating temp, choppy acceleration). since they are relatively minor in cost, i figure that replacing the parts are preventative since it does not look like they've been replaced in a long time if ever (thermostat, hi/lo aux fan switches, coolant temp switch, radiator hoses, flushing radiator, fuel pumps, fuel pressure regulator, spark plugs, O2 sensor, ICV, ICU). at least i changed the philips head screws on the TPS with allen headed screws to make it easier to remove and add a new one when I decide to.
i guess that is one suggestion that I haven't seen on these boards before is to replace easily stripped screws with bolt head or allen headed screws to make easier to replace parts, especially on routine maintenance items.
anyways, if anyone has any thoughts on my now intermittent choppy acceleration problem, I would be greatful. I do have one more question. There is no wire to pin 8 going to the ICU, but there is a wire going to pin 7 of the ICU. According to Bentley, pin 7 is for auto trans. position and you test it in park or neutral. I'm not sure what this does since i have a manual transmission. anyone have a clue of this or what pin 8 is supposed to do? I have '84 318i. thanks
i guess that is one suggestion that I haven't seen on these boards before is to replace easily stripped screws with bolt head or allen headed screws to make easier to replace parts, especially on routine maintenance items.
anyways, if anyone has any thoughts on my now intermittent choppy acceleration problem, I would be greatful. I do have one more question. There is no wire to pin 8 going to the ICU, but there is a wire going to pin 7 of the ICU. According to Bentley, pin 7 is for auto trans. position and you test it in park or neutral. I'm not sure what this does since i have a manual transmission. anyone have a clue of this or what pin 8 is supposed to do? I have '84 318i. thanks
Whoops, I also forgot to mention a huge leak under the motor due to a faulty oil pan gasket. It was so bad that oil would drip out of the car and it caused a lot of vacuum problems to boot. Starting, idling, and acceleration were all improved by this little $6 part, and an afternoon on the garage floor on my back 
)
)i have tested to AFMs and notice that both increase resistance smoothly until about half way open, then it drops smoothly. bentley says that resistance should increase until fully open, but i wonder if this is correct, since both AFMs do the exact same thing increasing then decreasing in resistance. anyone know?