Probably me, but it STILL does it.
I am sure the distributor is good, timed, functioning correctly. Switched the AFM once, no change. Switched thermo time, checked vacuum lines, grounds, new O2 sensor, pedal bushings, throttle switches good, set correctly.
If the pedal only works the linkage on the throttle body, ( clean, set up like new, correctly as per FAQ) what computerized thing can be making the pedal be so sensitive ?
Not smooth. Immediate on/off. Jerky adding throttle, (pedal, not stumbling or hesitation), letting off the pedal in second, bumping it can start a guibo bouncing hula. Less if I've unplugged the idle throttle switch, but that's not any cure all.
Nuts, ONLY because my '79 is smooth and what I know is normal.
Weird !
Throttle jerk.
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socalfiver
- Posts: 229
- Joined: Wed Jul 21, 2010 12:31 pm
- Location: Los Angeles, CA
throttle switches are set correctly, but what about the throttle plate? Cleaned and reset per FAQ? Boot between throttle and AFM in good shape and leak free?
Have you recalibrated the AFM? If the plate moves too easily, I could see it maybe making jerky response off idle.
Have you recalibrated the AFM? If the plate moves too easily, I could see it maybe making jerky response off idle.
"Get it while you can." -Janis Joplin
1980 528i Automatic, "Frau Blucher"
1982 BMW R100RS
1982 633csi 5 speed
1980 528i Automatic, "Frau Blucher"
1982 BMW R100RS
1982 633csi 5 speed
Thanks for the input, I'll check as directed.
A mechanic friend opined these cars ain't easy to diagnose. Older technology, milli volts, age, and my thinking is all carb, fuel needles, mixture, not the air being the adjusto variable.
Again, I don't get it, what thing or things happen to make the gas pedal so snappy, direct, bouncy. The idle cut off switch will do it: honk the horn with your nose if it clicks off early, but that's not what's happening.
A mechanic friend opined these cars ain't easy to diagnose. Older technology, milli volts, age, and my thinking is all carb, fuel needles, mixture, not the air being the adjusto variable.
Again, I don't get it, what thing or things happen to make the gas pedal so snappy, direct, bouncy. The idle cut off switch will do it: honk the horn with your nose if it clicks off early, but that's not what's happening.
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socalfiver
- Posts: 229
- Joined: Wed Jul 21, 2010 12:31 pm
- Location: Los Angeles, CA
Post says you switched AFM once with no change. That's probably not it.
Possible oxygen sensor came unplugged? I'm just thinking as an electrician... 99%of problems occur at the connections. Idle switch is supposed to slightly enrichen mixture (longer fuel spurt duration). That means, when the circuit is broken, it's supposed to lean out the mixture, which is where you are getting the jerky throttle. Idle and WOT switches both increase fuel duration. In between, you're supposed to be getting the Lambda mixture (metered by the oxygen sensor).
Idle speed is set with air bypass setting under the throttle body, and is reliant on the throttle plate being closed and the idle switch functioning properly. Make sure that throttle plate is fully closing and leaving you a 1.5mm gap at the top of the roller channel. Mine was incorrectly adjusted, and idle speed had been set with the throttle stop screw.
Possible oxygen sensor came unplugged? I'm just thinking as an electrician... 99%of problems occur at the connections. Idle switch is supposed to slightly enrichen mixture (longer fuel spurt duration). That means, when the circuit is broken, it's supposed to lean out the mixture, which is where you are getting the jerky throttle. Idle and WOT switches both increase fuel duration. In between, you're supposed to be getting the Lambda mixture (metered by the oxygen sensor).
Idle speed is set with air bypass setting under the throttle body, and is reliant on the throttle plate being closed and the idle switch functioning properly. Make sure that throttle plate is fully closing and leaving you a 1.5mm gap at the top of the roller channel. Mine was incorrectly adjusted, and idle speed had been set with the throttle stop screw.
"Get it while you can." -Janis Joplin
1980 528i Automatic, "Frau Blucher"
1982 BMW R100RS
1982 633csi 5 speed
1980 528i Automatic, "Frau Blucher"
1982 BMW R100RS
1982 633csi 5 speed
Thanks more. New oxygen sensor, no change from the old, plugged in.
I've done four throttle bodies (FAQ), but I'll check everything again if that's where the gremlin could be hiding.
My '79, set up by me, runs, feels normal. That's why this is so weird. I check, adjust, switch parts to match the '79 (except for the Aux air and vacuum retard tube), the '81 continues with the sensitive, direct, bouncy pedal. Of course I can drive it, by compensating with a smooth foot, clutch. I just know it's not right and I'm stubborn.
I've done four throttle bodies (FAQ), but I'll check everything again if that's where the gremlin could be hiding.
My '79, set up by me, runs, feels normal. That's why this is so weird. I check, adjust, switch parts to match the '79 (except for the Aux air and vacuum retard tube), the '81 continues with the sensitive, direct, bouncy pedal. Of course I can drive it, by compensating with a smooth foot, clutch. I just know it's not right and I'm stubborn.
IIRC 79 and 80 have both different ECUs and distributors. Either could play a role. Have you swapped those parts back and forth? And I think 79 had a vacuum retard line on the distributor and 80 did not.
Mike W.
02 525ita. Wife's, aka grocery getter
02 530i. New to the fleet, 3 pedals.
03 QX4, AKA the Datsun. Finally got the 4WD vacationmoble to stop smoking.
07 Xterra. Still on the DL, a purchase from hell.
02 525ita. Wife's, aka grocery getter
02 530i. New to the fleet, 3 pedals.
03 QX4, AKA the Datsun. Finally got the 4WD vacationmoble to stop smoking.
07 Xterra. Still on the DL, a purchase from hell.
For input, information, to solve the mystery, for anyone interested. The problem, is driveable enough to barely be one. Just be precise with pushing the gas pedal.
Certainly not arguing with any ideas, solutions. For info, I did not switch the ECU in the glove box. I did switch the wire harness, both pieces, carefully matching all the ends and wires. Exactly the same.
From collecting I have three distributors and AFM's. As picky, close inspection as possible, all are the same. realoem.com isn't great for model specific part numbers, these 3 and 3 are not identical part numbers.
All distributors have the retard vacuum pipe. It was for emissions, in '81 the throttle body pipe was capped, the distributor left open. Comparing, if there is a difference, it's way deep inside.
I'm going to take all the suggestions, reset, adjust, swap again. Something is adding, shutting off the fuel /air now, fast, instead of smooth.
Certainly not arguing with any ideas, solutions. For info, I did not switch the ECU in the glove box. I did switch the wire harness, both pieces, carefully matching all the ends and wires. Exactly the same.
From collecting I have three distributors and AFM's. As picky, close inspection as possible, all are the same. realoem.com isn't great for model specific part numbers, these 3 and 3 are not identical part numbers.
All distributors have the retard vacuum pipe. It was for emissions, in '81 the throttle body pipe was capped, the distributor left open. Comparing, if there is a difference, it's way deep inside.
I'm going to take all the suggestions, reset, adjust, swap again. Something is adding, shutting off the fuel /air now, fast, instead of smooth.
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marc79euro645
- Posts: 27
- Joined: Thu Dec 03, 2009 11:12 pm
Mark has a good point, if the weights are advancing off-idle without having to overcome the spring by inertia (normally) then you'd get full advance instantly (and probably a lurch!). That's why the vacuum advance is there, to sense manifold pressure changes when the throttle is opened and give you instant (limited) off-idle advance before the mechanical advance kicks in (and is affected by engine RPM). You might be getting both together.
I've suspected the distributor lately, looking at a vacuum advance issue but centrifugal advance could be an issue as well. I would suspect though servicing the mechanism by oiling (there is a felt wick inside the dizzy shaft that retains oil) would be more likely than a thrown or broken spring - the weight mechanism can get gummed up without service and not produce a smooth advance curve. I've had good luck with Aero Kroil spray (Kano Labs) just aiming some with the tube under the dizzy plate.
I've suspected the distributor lately, looking at a vacuum advance issue but centrifugal advance could be an issue as well. I would suspect though servicing the mechanism by oiling (there is a felt wick inside the dizzy shaft that retains oil) would be more likely than a thrown or broken spring - the weight mechanism can get gummed up without service and not produce a smooth advance curve. I've had good luck with Aero Kroil spray (Kano Labs) just aiming some with the tube under the dizzy plate.
HTH
'80 528i
'80 528i
I have the list of things to check, recheck. One of the things is to find out if two or three distributors, AFM's can have the same problems. So far, swapping both haven't changed anything.
Maybe we all know, how, after awhile, it's fun to write in and ask what to do. Someday. But there's ten things and it runs, so just drive it.
If not, screw me. I appreciate the solutions, to yell Eurika ! when one works.
Maybe we all know, how, after awhile, it's fun to write in and ask what to do. Someday. But there's ten things and it runs, so just drive it.
If not, screw me. I appreciate the solutions, to yell Eurika ! when one works.
Don't give up...you will find it.T.Hanson wrote:I have the list of things to check, recheck. One of the things is to find out if two or three distributors, AFM's can have the same problems. So far, swapping both haven't changed anything.
Maybe we all know, how, after awhile, it's fun to write in and ask what to do. Someday. But there's ten things and it runs, so just drive it.
If not, screw me. I appreciate the solutions, to yell Eurika ! when one works.
1977 BMW 530i
1973 R75/5 BMW (motorcycle)
1973 R75/5 BMW (motorcycle)
Thanks for the input from an old post. I'd checked the throttle switches.
Turned out to be the AFM, which threw me off by replacing it with a spare that did the same thing. As I concluded a jerky throttle had to be caused by something darn close to where the throttle lever connects to the associated contraptions, I changed to a third spare AFM and it runs smooth. Go figure.
It was doing the idle zoom, drop routine. Took the valve cover mounted aux air valve off, cleaned with carb cleaner and rust blaster. Adjusted the little nut to allow the baffle to almost close completely. ( Less air, richer on cold start ups.) Must've been right. Workin' great.
Turned out to be the AFM, which threw me off by replacing it with a spare that did the same thing. As I concluded a jerky throttle had to be caused by something darn close to where the throttle lever connects to the associated contraptions, I changed to a third spare AFM and it runs smooth. Go figure.
It was doing the idle zoom, drop routine. Took the valve cover mounted aux air valve off, cleaned with carb cleaner and rust blaster. Adjusted the little nut to allow the baffle to almost close completely. ( Less air, richer on cold start ups.) Must've been right. Workin' great.