Help - runs rough for first 15 miles

[Trickie Dickie]

I am having an intermittant engine problem on my 1989 350i and wondered if anyone has had similar problem that they managed to solve.
The problem started after a 30 mile run - just as I got home it started spluttering a bit. (I thought it was due to the last 2 miles being thru 4 Gatsos at 30 mph!!!!!). But now each run out it splutters for upto 15 miles then all clear and runs perfectly (ask Tallbloke who at times last week struggled to keep up).Lately I think it has also kicked in again later on a longer run out.
I say kicked in because 1 minute it is bad and the next totally clear.
When it is bad, the tickover drops considerably(but isn't erratic), it becomes very difficult to drive in traffic due to the jerkiness, but all the power is still there when you "floor it".
I have also noticed that the popping and lovely noises we get from our Wedgies on over-run stop when it is running badly.
The car is fully serviced and had new leads and plugs, (it certainly doesn't feel like a cylinder not working). I have filled up a couple of times (always with Optimax), and having talked to several people now feel the problem is 1 of the 3 heat type sensors on the engine.
Can anyone please help me as to what this can be?
Many thanks
Richard (Dark Brown 350i Wedge)

[chassis 33]

Have you changed the fuel filter? It could be crudded up and occasionally free, hence the rough running, hit a bump and it clears itself?

Regards
Iain

[number 7]

I've experienced similar intermittent problems: fuel smell when running, no idle, lack of soundtrack. I initially thought it was the corroded state of the wiring/connectors near the fuel pump, so changed all of those. Finally noticed that the fuel pump relay was getting extremely hot, caused by disintigrating wiring to one of the pins on the relay board. Renewed connectors to all pins on that relay cured the problem.

7.

[Trickie Dickie]

chassis 33 said:

Have you changed the fuel filter? It could be crudded up and occasionally free, hence the rough running, hit a bump and it clears itself? Regards Iain

Thanks for this Iain, I will check the fuel filter etc but I think the problem is more temperature and switch triggered rather than cleared by a bump etc.

[Trickie Dickie]

number 7 said:

I've experienced similar intermittent problems: fuel smell when running, no idle, lack of soundtrack. I initially thought it was the corroded state of the wiring/connectors near the fuel pump, so changed all of those. Finally noticed that the fuel pump relay was getting extremely hot, caused by disintigrating wiring to one of the pins on the relay board. Renewed connectors to all pins on that relay cured the problem. 7.

Thanks again - but seems more of a problem from start up than just on/off intermittantly. It does idle but at a much lower rpm say 600 rather than 900rpm. I don't have any smell of Fuel.

[number 7]

is the cold start injector connected ? Lots of people disconnect them completely.

7.

[grahamw48]

My 390 takes ages to warm up now, with the colder weather, and runs 'rough' if full welly is applied before proper running temperature is reached. Fine after that though.
It can take quite a few miles if out of town, but I don't think 15.

[dickymint]

coolant temperature sender? cheap (£12) seems to be a pre-requisite before doing anything else.

[tallbloke]

Suspect number 1:
Coolant temp sensor

I learned this the other day on my Rangie thread.

Oh, and I wasn't struggling to keep up, I was taking it easy because of that suspect wheel bearing.

Having said that, you've probably got around 15bhp more and about 30kgs less, though your pasenger would have made up more than that.

Mine is set up fairly softly at the moment for running in. I'll race you next year once I've got the turbo on though.


>> Edited by tallbloke on Tuesday 25th October 00:11

[Trickie Dickie]

Thanks again guys

Its going in the garage on Monday anyway
hopefully for the rollcage fitting, and will
get them to check other suggestions

Thanks

Richard

PS Tallbloke - I'm not racing you when your turbo is fitted - you kept with me far too well before!!