This is my first post on this forum; however, don't let that cloud your judgment when it comes to my love for the e34. I own a 1995 525i with an automatic transmission and 167k miles on it. I have had the car for 2+ years now and despite some hard times; I will never own a domestic pos ever again. About 6 months ago I started to experience some hesitation (felt almost like it was missing) during acceleration. At first it wasn't too serious of a problem, but it got to the point that I had to do something about it. I am a college student and have no money, and I also hate letting anybody touch my car so I started to self diagnose. Found that my valve cover gasket needed to be replaced because it was leaking oil onto my spark plugs. Replaced the gasket, spark plugs, and air filter. The problem got better, but was not completely gone. Checked to make sure the gasket was good, and everything was fine.

When I started the car on cold mornings the car had no hesitation and was faster then I could remember. After about 2-3 hard accelerations the vibration was back. If I would barely push the acceleration pedal it wouldn't vibrate, and if I floored it I couldn't feel it or hear it also. However if I tried to accelerate hard without the car downshifting, the car would begin to vibrate. I went awhile with this problem and just drove it in a manner that prevented the vibrations.

A week ago the gas pedal gave out and I fortunately was pulling into my driveway. The CEL came on and It gave me the code for the O2 sensor. I had a feeling that this could have been the cause of the vibrations to begin with so I was a bit excited. I changed the O2 sensor and the fuel filter and then found that the car still wouldn't start. That is when I found that the car wasn't getting any gas from the tank. Checked the fuel pump relay, and it was good so I replaced the pump with one I got from a junkyard. It was off a low mileage 95 525i and it actually wasn't the factory original so it is in pretty good condition. The car started right up, but sounded like shit. I thought it would get better after I drove it around for a bit so I did. It did get better for a while so I drove it to my girlfriends house 30 minutes away.

After about 10 minutes of driving I began to regret it because it was significantly worse then before. Only really vibrating when I had to go uphill. When I got into town i noticed at stoplights that the hesitation-missing increased when the auxiliary fan kicked in, leading me to believe that it might be an electrical problem. This morning when i was leaving the girlfriends the car started up crappy again and once I left her neighborhood it acted like there was nothing wrong. Acceleration was great and the car felt amazing. Stopped to get breakfast and when I got back in the car it was driving a little worse. By the time the car started to reach normal temp it was driving like crap again.

I am totally blown away by how temperamental the car is, and also frustrated that I can't figure out what is going on. My last guess is that because of the high mileage and initial leaking of the valve cover gasket that it could be the ignition coils are going bad. Other then that all I can think is the ECU, which would really suck. I am hoping that somebody knows exactly what this could be, or at least point me in the right direction. Sorry for the long post, you guys have been a great deal of help in the past just by surfing your forum, hopefully you can be a great help to me now.

sounds like mabey the coils or coolant temp senso or a combination of the two. Also could be the MAF but i would check the other two first.

oh yea, he has an M50 so no ignition wires ;)

There is a sensor that says that my coolant level is low, but I just got my radiator replaced about 8 months ago and the mechanic said that it would be another 100 dollars or so to get that replaced. He also said if I chose not to that it was no big deal, and more of an annoyance than anything.

Im not familiar with a rotor / cap. Forgot to mention that I cleaned the MAF with some of that MAF Cleaner

Dude... :eek: Paragraphs please or point form. This is like a big lump of words

Have you changed the ignition wires and rotor / cap? Spray a little water on the wires while the car is running and see if the misfiring begins. Check their impedance with a multimeter. Sounds like arcing of your spark somewhere. My 2 cents

lollerskates, it' an M50, no sodding rotors or plug wires

I'd definitely meter out or try changing the coolant temp sensor for the ECU.

First off, welcome to our little slice of the internet. :)

If it is indeed the ECU, that's probably the least costly item to replace ... they can be found used for ~100 on ebay.

That said, it could be the throttle position sensor, coils, ecu, or mass air flow sensor.

I'll try to link you to a Bentley service manual you can download that will help you test and troubleshoot all these things ... just give me a few minutes.

Dude... :eek: Paragraphs please or point form. This is like a big lump of words

Have you changed the ignition wires and rotor / cap? Spray a little water on the wires while the car is running and see if the misfiring begins. Check their impedance with a multimeter. Sounds like arcing of your spark somewhere. My 2 centsIt's a m50tu ... it is coil on plug. no wires etc.

If it is a 95 you have coil on plug not cap and rotor. and I think you are on the right track with a coil being bad. you can either buy a new one and keep swaping it to different cyl untill the problem goes away unless it is multiple coils. or go to a good shop and have them check it out and they will find out for sure.

http://luuk.xs4all.nl/bmwboeken/Bentley_BMW_5-Series_Service_Manual.pdf

amazing... you have no idea how long i have been putting off buying one.

Before you go any further, check the voltage of your car's system. Check it with a multimeter across the battery terminals with the ignition off, then with the car running. You can also monitor the voltage while the car is running through the OBC. Do a search, I'm sure you will be able to find the procedure if you don't already know how to do that.

Let us know what the readings are with ignition off and with the engine running. Let's make sure you are getting enough juice to the coils first.

i saw that slocar said that I have a M50tu, was wondering how you know this and if that is for sure seeing how the diagnosis for the MAF is different for the M50 and M50tu

M50 (non vanos) was 92 and late 91. The M50tu (vanos) was after that so 95 = M50tu

I checked the voltage across the battery terminal like you said. The voltage with the car off is 12.6. With the car on with everything running (A/C, Radio) ranged from 13.5 to 14 depending on whether the auxiliary fan is on or not.

Your voltage is alright. Mine is in that range as well with the car running.

As far as diagnosing the MAF differences for m50 and m50tu, I'm not too sure ... I know the MAF itself is different; the Bentley should cover how to test both though.

I had a similar issue and it was a vacuum leak

I checked the voltage across the battery terminal like you said. The voltage with the car off is 12.6. With the car on with everything running (A/C, Radio) ranged from 13.5 to 14 depending on whether the auxiliary fan is on or not.

That's good. That is right where it should be. You can now rule out the battery, alternator, grounds, etc. Your electrical system is producing plenty of juice.

I agree with boilerman, you should look to vacuum leaks next.

What exactly is a vacuum leak?

The ECU takes readings from the MAF or MAS so that it knows how much air is entering the intake. It uses this to properly adjust the air/fuel mixture going into the cylinders. If air enters after the MAF, the computer can't measure it so it throws the mixture off causing the engine to run lean or rich.

Most of the rubber intake hoses are between the MAF and the engine. As they get old, they get brittle and crack. When they do, they let unmetered air into the intake and throw off the air/fuel mixture in the cylinders. It will usually throw a code for an o2 sensor lean/rich mixture error.

well i just went out to the car and listened to the engine with the hood open, and didn't really notice any hissing, so i played with the throttle some. When i slowly gave it gas everything seemed to be smooth, but when i would quickly give it some gas the car will stumble and there is a pretty loud sucking noise coming from somewhere around the throttle body. Its really hard to pinpoint, but im going to go ahead and assume that I have a vacuum leak somewhere.

I also have been looking over the Bentley manual and when checking to see if an electrical part is functioning it usually asks for you to disconnect the harness from the part you are wanting to test, then to measure the voltage and ohms across different terminals on the harness. I don't see how doing measurments on the harness will tell you if the part is good or not. If the measurments from the harness are bad wouldn't this mean that there is something wrong somewhere else and not at the part? Or am i supposed to figure out which terminal which wire goes to, then test the wires with everything plugged back in. Am i missing something?

Is the vibration coming from the cylinders? If not it could be a pulley or something like that but if it is could be a misfire but you should be getting a Check Engine Light for that. Are you still getting a hestitation? Also a lot of people spray like starting fluid or something like that to detect a vacum leak.

Well, the first obvious thing to check for a vacuum leak is the big intake boot that runs from the back of the MAF to the throttle body. Take the hose clamps off and remove it. Inspect it for cracks, especially the points where the hose claps sit. If it's not obvious, it may be another smaller hose or the gasket around the throttle body or intake manifold.

The best way to truly pinpoint it is to get one of those little propane bottles that you can buy for portable grills or plumbers torches. Get a piece of flexible hose and turn the gas on. Don't light it obviously, just let the gas flow out. Spray the gas around all the connections for the hoses, and around the different intake gaskets. If the idle picks up, you have found your leak.

You can use throttle body cleaner too, but it makes a bigger mess.

Well...I took care of what i thought was the vacuum leak. The main intake boot has the two little hoses running off of it. At those two points there were some pretty bad cracks so I went to the dealer and got a new boot and replaced it. Unfortunately it didn't fix the problem.

When the car is in neutral I can rev the engine slowly and it is very smooth. If I make any sudden movements with the pedal the car misses badly.

If you guys still think it’s a vacuum leak I will probably just take it to this guy I know. So let me know

I am wanting to check everything else on the car to make sure it isn’t something else so could somebody give me an answer to my previous question about checking voltages and ohms across wiring harnesses.

One other thing... After I replaced the fuel pump, O2 sensor, and fuel filter I have been getting 16.6 mpg. I was getting 21 before.

Check your FPR "Fuel Pressure Regulator", it might not keeping the required pressure. It seems when you give sudden or abrupt fuel when you press your gas pedal it bogs your engine or stumbles it. Flooding it.

is there any way to "check" it or do I have to just replace it?

Im sure you guys are tired of this thread, but I need just a couple more questions answered.

1. Ignition Coils

a. Tested ohms on each coil and every single one gave me a reading of 0. The reading would jump around everywhere for a couple of seconds then end up at 0. Does this mean they are bad? I have 160k miles on my car, but I have heard coils really dont go bad.

b. Most all of the boots on my iginition coils are badly cracked. Would this cause the problems I am experiancing?

c. Should I just replace the boots or the entire coil

2. Fuel Pressure Regulator

a. Does this sound like a likely problem? I have been getting horrible gas mileage since I replaced my fuel filter and pump. Along with the decrease in engine performance.

Thanks.

Ignition coils....wow, I don't know who's been feeding you info, but coils can and do fail all the time. Especially on M50s and M60s.

You should never read 0 ohms on a good coil. However, an inaccurate or low-quality meter might think so...the value you're looking for is .4-.8 ohms.

Yes, badly cracked coil 'boots' should be replaced. Yes, bad boots and/or bad coils can certainly cause poor performance and mileage. If the coils test out ok, they are probably ok, but even bad coils can test good when cold.