Engine running rough and shaking badly at idle and at higher rpm too, hot /cold

[alex 1993 525i auto]

Hi there,

My 93 525i was running great all year long before. Saturday night after dinner 50 miles away, started the car to go back home. Obvious rough running and engine making the entire car shaking, but no Check Engine Light (CEL) signal. Once engine hot, no change, while driving it was quite less powerfull and I could hear it and feel it strugle under the gas pedal when accelerating, like if it was missing on some cylinders (but I never experienced that so hard to tell now).

It ran bad like that but I drove it home 50 miles without other problems. On next morning I checked with my Peake tool to see if codes were stored and no codes. I confirmed with the pedal stump test and only code 1444 shows continuously = no codes. Started the engine and it was still shaking badly and running rough. Let it warm up a few minutes and checked by hand that all 6 exhaust ports were as hot one compared to each other, and all 6 were very hot, no difference between any.

I stopped the engine, removed the fan clutch to see if it was the problem and no, same behaviour without the fan clutch. Then I removed both belts, started again the engine and no difference, so it doesn't look like it is something driven by the accessory belts.

I disconnected the MAF socket and started the engine again, the CEL signal appeared right away, but otherwise no difference, still running bad and shaking. Then I repluged the MAF and checked that every vacuum hose was correctly set and everything was where it should be and no worn broken hoses were seen.

In the 4 last years, all vacuum hoses, intake manifold gaskets, throttle body gasket, MAF, O2 senson, coolant temp sensor, idle speed control valve (ICV), spark plugs were replaced. Passed smog test 3 years ago too in California. Also 3 years ago fuel pump with fuel level sender, fuel pressure regulator, fuel pump relay and fuel filter were replaced after fuel level sender failure. This year I replaced the vanos piston seal along with diaphragm spring upgrade on the intake camshaft, valve cover gasket, lower timing chain tensionner, engine doesn't burn any oil and was running great but pinging under load. This summer I also tested compression and each cylinder was at 160 psi, spark plugs were clean. One month ago I decarbonized the combustion chamber to some extent that it doesn't ping anymore, with Seafoam added by the small vacuum hose from the PCV valve. Fumigated the entire neighboorhood by doing that. Battery is 3 year old and seems fine, alternator was rebuilded this summer.

I searched a lot here and on bimmerboard to find insights to what could be wrong now. Most posts say either MAF or ICV or CPS, or fuel related, or coils and spark related. I doubt that MAF, ICV, or fuel related part is wrong because those were replaced recently and with a bad CPS the car should not start at all. Also again, there are no CEL warning.

Next Saturday I'll look at the spark plugs first, maybe test the coils. I read that it is possible that the ICV could block 'mechanically' and that would not be seen by the OBC. I also read a post from a guy that had a broken intake valve and the simptoms were kind of similar to mine. I will see that when I check at the spark plugs I guess it will be obvious on the plug, if not a compression test will tell me.

Any other ideas from the mechanical gurus here?

Thanks, Alex

525i 1993 (built 05), M50TU, auto, 231k miles

[bubba966]

Check part #9 in this diagram
http://www.realoem.com/bmw/showparts...24&hg=11&fg=40

It's the plastic connector that connects the rubber ICV tube to the intake manifold. The crappy plastic retaining clip on it breaks frequently causing it to back itself out of the intake causing a large vac leak that will cause the engine to run terribly if at all.

Easiest way to check it is to pull the throttle body off the intake and look into the intake through the hole to the throttle body. That connector plugs into the intake right behind the throttle body and is easily seen as it's quite large.

Should be about a $6 part at the dealer. They probably stock it as well do to the frequency of it breaking. I know my local dealer had it in stock...

[alex 1993 525i auto]

I've seen a post very similar to your suggestion (maybe it was you telling that to someone else) and when I look at the vacuum hoses in the intake area I had a look at that particular one, but it is tight on the manifold and ICV. I'll double check anyway Saturday when I'll check at the spark plugs and try to identify the problem again.

If you (or anyone else) have another idea let me know please! Alex

[genphreak]

The pipe to the ICV splits, you really need to check that too. The first pipe to go I think is the fuel pressure regulator vacuum hose, right at the back of the intake manifold. It comes from a connector under the manifold that is reliable. This hose splits and perishes with age...

[Marcusd]

My partners 525i has started behaving in the same way a couple of days ago. This last happened to her E34 a couple of years ago at the same time of year when it got cold outside.

I thought it may have been a cracked block or head gasket problem as it idled really rough, the coolant was a little bit low and it would die if you try to give it any throttle. At the time I put a couple of bottles of K-Seal "miracle cure in a bottle stuff" into the top hose and removed the thermostat. This did not seem to do anything to help at first but when we left the car for a couple of weeks the fault mysterioulsly dissappeared. This was nearly 20,000 miles and 2 years ago. Now the fault has returned.

I have put another couple of bottles of K-Seal in again and it is still running roughly. This always seems to happen when the weather turns cold and we have left the car without using it for a week or two.

Having read your post it sounds exaclty like the problem we have with one of our E34's. I will check the hoses and if I find anything I will post back.

Good luck finding your rough running issue.

Cheers, Marcus

1995 E34 525i 242,000 miles (good)
1995 E34 535i 182,000 miles (running rough at the moment)!

[Marcusd]

Just had a look at mine. The hoses all seem ok with no apparent leaks. I can only get it to rev with this problem by being very gently with the throttle.
I had a look at the fuel pump in the top of the petrol tank, from the panel under the boot (trunk) carpet. It did not seem to make any noise when the engine was running where as our other E34 has a faint humming noise coming from it.

I had a poke around with the connectors and it seems to have brought the pump back into life and cured the problem for now. The connectors were not loose so I am guessing that the drop pump in the tank is on it's way out. Maybe me poking around just freed it for now.

Alex, I know your fuel pump was replaced 3 years ago but is there a quick way you can test your tank pump as your problem sounds very similar to mine? Maybe it could be the relay or wiring to the pump? Once it was going the hoses on the top of the pump felt to have more pressure in them and I can hear the pump now. The car is back to running spot on for now.....

[alex 1993 525i auto]

After reading the last 3 posts:

Thanks Genphreak I'll have a look too at the vacuum hose attached to the FPR.

Hey Marcusd, not so sure about all what your saying... 1st I would avoid over-using that K-seal in the coolant liquid, it might change the properties of the liquid and modify the heat capacity of the coolant and also the micro-ceramic they say will cure leaks might also dirty your thermostat, water pump, radiator and heater core. To verify for a cracked head/block/head-gasket 1st thing is to check the aspect of your oil and coolant. If no oil in coolant (brown droplets on top of coolant) and if no coolant in oil (makes a beige-brown residue on the dipstick) than no cross-contamination occurs. Then the cylinder compression test will tell you if one cylinder (or the valves on that cylinder) is leaking. For your cold start rough idle issue, it could be worn intake manifold gaskets which cause a vacuum leak on cold start, and when the engine gets hotter the heat make them swell and seal as it should when hot. Then you mention that upon playing with the connectors on the fuel pump that it revived your car for now. Below that connector is the fuel level sending (FLS) unit and below that is the fuel pump. In my case it was the FLS witch was worn, testing the resistance on the connector as in the Bentley manual showed this was wrong, not the fuel pump, but I replaced both anyways. If that resistance is not in the good range the current doesn't pass enough to power the fuel pump. Maybe you should check that too. When it happened to me it was intermitent for a few weeks, letting me stranded twice, than restarted after 0.5 - 1 hour. Than it failed for good. Hope it helps. I'll check the my problem is fuel related too once I confirm it is not spark or engine related.

[genphreak]

Yikes! IMHO: If you remove a thermostat on an e34, any e34, or any modern bimmer, and it actually improves the presenting problem/s, you are simply addressing the symptoms of a serious cooling system problem that will sooner, rather than later cause a major 'head'ache... these cars have carefully designed cooling systems designed to maintain engine performance through very carefully considered temperture management in all extremes. As an owner, one has no choice but to maintain it with proper care, especially if the PO did not... and particuallry if they experienced even the most basic of cooling problems.

[Marcusd]

Sorry, forget the K-Seal cracked block thing, this looks like it was just bad diagnosis on my part. When we had this problem before 2 years ago the coolant looked low so even though there was no oil in the water or vice versa, I presumed the block had a crack somewhere. After adding a bottle of K-Seal and leaving the car for a couple of weeks the fault disappeared and the car has been fine for the last 2 years. When the fauly reappeared I presumed that adding another bottle of K-Seal would solve it.
Once I had realised that this problem was something else I looked on the forum and this post was the first post and a near identical problem to mine. I removed the thermostat on this car as it jammed open and could have killed the engine. The thermostat on my engine has been jammed open for years so I have just left it. I know really that I should replace them but with the cars being in the UK, all that really happens is that it takes a little longer to warm up in the morning on cold days, there is no risk of it jamming shut and cooking the engine.

I am going to have another look at the problem today but suspect the fuel pump as my issue has gone for now after fiddling with the pump. As Alex's issue sounds so similar to mine I just wondered if it would be worth him double checking that the fuel pump, relay and regulator are working properly.

[Marcusd]

Thanks for the info Alex, I will dig out my Bentley manual and check the resistance on the FLS.