Crappy idle and jerky throttle response after new injectors and TPS

[E turd]

UPDATE: The idle and accelerations problems seem to have disappeared, but the car is running pretty rich and when the car is stopped at a light and idling, after a few seconds the check engine light comes on. It stays on until I push the accelerator pedal and then it goes away. Today I installed the chip and things are unchanged. I did notice that the car seems to lag worse than usual when I step on it until about 4000 rpms. I know usually people say coolant temp sensor or oxygen sensor, but it seems too coincidental to be either of those since I wasn't having any problems prior to this wave of part installation.


Recently I installed some E36 17.5 injectors and a new TPS. The car seemed fine for the first few drives, then the check engine light starting coming on for just a second (happened like 3 times during different driving sessions). Now the idle is all over the place and when I give the car gas it will feel normal and accelerate, then jerk backward like someone has cut off the fuel or stabbed the clutch all of sudden. It will alternate between jerking forward (positive/normal throttle response) and back (no throttle response). I imagine is has to be something I did wrong, but I can't figure it out. I had a look over the motor a few times looking for vacuum leaks or cracked hoses and all I could find was some cracks in the little hose that goes from the idle stabilizer valve to the throttle body so I replaced it with a new one. After that the problem is persisting.


Is it possible that it's behaving like it is because it needs a chip for the new injectors? I wasn't having any of these problems before I replaced the injectors and tps. I am also fairly certain that the TPS is properly adjusted. I followed the protocol in the Bentley so that the two pins show 0 ohms and I also looked at the marks left by the mounting screws on the old unit and they appear to be in the same place so I don't think it's the TPS, but I am human so I could have effed up somewhere.


The car is a 1990 325i w/ manual transmission. Any ideas about what might be going on here? I have a Mark D chip on order and am just waiting for it to get here.


Thanks in advance!

[jlevie]

You don't say what year car, but if an 88 or later check the condition of the C191 connector under the intake manifold.

[E turd]

You don't say what year car, but if an 88 or later check the condition of the C191 connector under the intake manifold.

It says in the last paragraph that the car is a 1990 325i. Anyone else?

[nando]

do you have a working o2 sensor? this is pretty much the only way the ECU can adjust for the bigger injectors, so if it's not working it will run rich.

[E turd]

O2 sensor was tested today and is working well. It appears that the car is actually running lean and after the 02 sensor tries to compensate, the net result is a rich condition. My mechanic friend (read mechanic as in owns and operates his own shop for longer than I have been alive), adjusted the fuel mixture screw at the MAF as a short term band-aid until I can trouble shoot the new injectors and the injector harness. There is also a misfire in one or two cylinders which might be caused by an injector opening late (misfire was present prior to installation of bigger injectors, so might be unrelated). After looking at it the consensus was that it could be a vacuum leak, bad ISV, bad injector, bad injector harness or connector. Essentially what seems to be happening is that the engine is receiving more air than it should be so it's running lean. During idle, the ECU and o2 sensor compensate for the lean condition, but as soon as I give it gas the lean condition returns causing sluggishness until 4k. At least that's the way I understood it.


I am just confused as to why the injectors are suspect at all. I had the guys at cruzin performance test, clean and rebuild them so it seems strange that the problem could be caused by an injector, but I guess stranger things have happened. Since adjusting the mixture at the MAF, the check engine light has not come on again.


My friend also loaned me a book put out by Bentley Publishers about Bosch Motronic injection systems so I guess I'll be doing some reading. He also recommended that I pull the plugs and look to see if any are noticeably different looking than the others. He also suggested that if there was one or two that looked different to try switching the injectors to different cylinders and see if the problem follows the injector or stays in the cylinder. I'll probably try to do this stuff tomorrow when I have more time and daylight.

[Adrian_Visser]

Your hypothesis about it running lean is flawed. The DME runs closed loop at idle that means that it isn't using the real time signal from the O2 sensor to adjust the mixture, that said however the 173 and later dme's can change the base values over time which affect the closed loop mode.

Also the "mixture screw" that your mechanic friend adjusted is the idle CO adjustment srew and only affects the idle mixture, the adjustment for the AFM is under the black plastic cover it is a trim wheel which changes the output voltage of the AFM potentiometer.

How was the O2 sensor tested? I always thought that testing an O2 sensor with a DMM wasn't very accurate.

[E turd]

Thanks for the corrections. I am by no means any kind of master when it comes to fuel systems or diagnosis/troubleshooting in general. Hopefully when I am done reading the book my friend gave me I'll be a little more capable, though.


In response to the question about testing the o2 sensor, we put a multimeter on the black wire of the o2 sensor after it was unplugged. According to my friend, if the sensor is working you will see the values fluctuate from .2 to .8 and back, and you will see that fluctuation happen more rapidly when the throttle is depressed. We also shot some carb cleaner into the little vacuum port on the intake manifold where the hose that comes from the FPR would go and the sensor would read .8 (rich, as I was told).



Oh, and BTW I do have the 173 DME in case it wasn't obvious.

[E turd]

Update #2: The jerky throttle response (also known as bogging, I think) is back and worse than before. The car idles fine and doesn't seem out of the norm when there is no load on the vehicle, but when I push the accelerator pedal, the car bogs pretty badly. Power is not what it should be and gas mileage is still in the crapper. I noticed it bogs worse in the 2.5 to 4k range. I installed new sensors on the T-stat housing (thinking they might have been bad or on their way out before I installed the +1 injectors), and also put in a new CPS. The old one had some of the wire coating worn away by the radiator fan and the metal was showing so I thought for sure that the problem must have been that, but there has been no change since replacing the 3 sensors.


At this point I am kind of at a loss. It seems like it could be so many things such as:

-bad MAF
-vacuum leak (which I have looked for several times and not found any yet)
-bad DCM
-bad injector(s)
-bad injector harness
-separated crank pulley center section


I have very little experience diagnosing this sort of thing and really don't want to waste the money taking it to a shop so they can tell me to replace the aforementioned parts one by one until it hopefully takes care of the problem. I am close to just putting the nasty original injectors and stock chip back, but the notion pains me deeply since I spent quite a bit of money on the refurb for the injectors and the Mark D chip.

When I was researching injector upgrade options, one of the forum wise men said that upgrading injectors will just magnify an existing problem. Well, I guess it's true because the bogging used to only occur in the morning when the car was cold and it would go away. Now it's present all the time. Knowing the bogging was present before the injectors, new TPS, and chip were installed, it's hard for me to figure out if the current poor state of running I am experiencing is a result of something I did wrong/broke, or if it's magnification of a pre-existing problem.


What say you, o wise forum?

[Knockenwelle]

Where did you source the TPS? Is it a Bosch part? If not, make sure it is before proceeding any further.

You may also want to swap the AFM with a known-good unit (borrow from an E30 buddy...) just to rule that out, too.

IMHO, your problem is due to the injector size. Although it doesn't seem like a lot (3lb/hr), you have increased the flow rate by 20.6%, which is a substantial jump. Without AFM correction, the default fuel table will provide way too much fuel. In closed-loop mode, the computer will see this via the O2 sensor, and subtract injector trim until either it sees target idle and part-throttle mixtures, or hits the trim limit. In my experience, the computer puts more emphasis on part-throttle trimming, which in your case, would lead to a lean idle. Try unplugging the O2 sensor and resetting the computer (disconnect power).

So, you need to:
1-confirm that you have a Bosch TPS
2-swap your AFM to see if that has any effect. The potentiometer wiper insode DOES wear out.
3-Disconnect O2 sensor and verify rich idle and part-throttle mixture.
4-Install your chip, which should correct the fuel table. If the problem persists, see #5.
5-adjust (or replace with M30 version and adjust) the AFM (after chip) to provide correct part-throttle mixture.

[E30Nova]

You don't say what year car, but if an 88 or later check the condition of the C191 connector under the intake manifold.

Seriously, check this. I had the EXACT same problem after installing bigger injectors and a chip. I figured it had to be the chip and/or injectors or a vacuum leak.

Ended up being corrosion at the C191 connector.

Matt

[jlevie]

What I'd do at this point would be to have the intake and crankcase smoke tested to see if there are any intake leaks and I'd run the suite of fuel system tests in the Bentley manual.

[E turd]

Where did you source the TPS?

The TPS is indeed a new Bosch unit.

You may also want to swap the AFM with a known-good unit (borrow from an E30 buddy...) just to rule that out, too.

I don't have any buddies with E30's to borrow from. I am the only guy in town who owns a performance oriented/tuner one of these for at least 15 miles and even then I wouldn't know where to look since there aren't exactly any local GTG's on this side of the hill.

IMHO, your problem is due to the injector size. Although it doesn't seem like a lot (3lb/hr), you have increased the flow rate by 20.6%, which is a substantial jump. Without AFM correction, the default fuel table will provide way too much fuel. In closed-loop mode, the computer will see this via the O2 sensor, and subtract injector trim until either it sees target idle and part-throttle mixtures, or hits the trim limit. In my experience, the computer puts more emphasis on part-throttle trimming, which in your case, would lead to a lean idle. Try unplugging the O2 sensor and resetting the computer (disconnect power).

I respect and value your opinion, but I read in many other threads prior to upgrading the injectors where guys ran these same injectors w/o even a chip and didn't have the bogging problems I am having. I know every car is different, but it just seems like the car shouldn't be this bad. Plus, the Mark D chip has been installed for a few weeks now and nothing has changed. I will try to unplug the 02 sensor and resetting the computer per your recommendation.


On the note of the AFM, is it better to run the m30 version? When I was researching the injector upgrade it was mentioned several times, but it's not mentioned as being needed on the Mark D site and in many of the thread I read about, it seemed like the m30 AFM was a waste of time. Of course, I am open to changing it out in the interest of better running conditions, just want to be sure it's necessary.

So, you need to:
1-confirm that you have a Bosch TPS check
2-swap your AFM to see if that has any effect. The potentiometer wiper insode DOES wear out. Will try to find one
3-Disconnect O2 sensor and verify rich idle and part-throttle mixture. How do I verify this? I have a DMM,. but I haven't used it much and don't have any formal training on it's functions and when the use them.
4-Install your chip, which should correct the fuel table. If the problem persists, see #5. Chip is already installed
5-adjust (or replace with M30 version and adjust) the AFM (after chip) to provide correct part-throttle mixture.

[E turd]

Seriously, check this. I had the EXACT same problem after installing bigger injectors and a chip. I figured it had to be the chip and/or injectors or a vacuum leak.

Ended up being corrosion at the C191 connector.

Matt

I will definitely check this out tomorrow. I wish I could have the same luck as you and that this could be my problem. However, since it's a California car I am doubtful. Nonetheless, what did you do to fix your problem. Clean with electronic connector cleaner? Apply dielectric grease? Wire brush?

[SpecM]

Clean with electronic connector cleaner? Apply dielectric grease?

those two ^

I wouldn't mess with the m30 afm, they can be more trouble then they will ever "solve"

[E30Nova]

I will definitely check this out tomorrow. I wish I could have the same luck as you and that this could be my problem. However, since it's a California car I am doubtful. Nonetheless, what did you do to fix your problem. Clean with electronic connector cleaner? Apply dielectric grease? Wire brush?

Mine is a California car as well, so I was surprised to see corrosion in there. I just used a wire brush and sand paper since that's all I had. Then I blew it out with compressed air.

Matt