E34 spark plugs.

[tetleysmooth]

I've got an E34 525i with the m20 engine. It's an F reg, with the later Motronic system.
What are the best sparkplugs to use?
I've heard different people saying a certain plug is the best, so what are your opinions please?
Thanks people.
p.s. my local car shop only sells NGK, any good?

[Rav335uk]

I used to use NGK, but found Bosch to be ok, numbers not to hand, and a very good set of leads too

[tetleysmooth]

Cheers Rav.
I've had a problem with this car since buying it. It had/has bad hesitation when the engine's cold. I've replaced the coolant temp sensor now, and it seems a bit better, but still splutters a bit on start up, hence me asking about plugs.
Also, kind of related, apparently the ecu stores fault codes. Would this alter the running of the car if the fault codes are not cleared?
Is it possible to clear the fault codes myself, or do they need to be cleared proffessionally, i.e. plugged into a computer?
Sorry about my thickness, but I'm rather new to this electrickery.

[Andyboy]

Early E34's and E30's with the post 87 Motronic system did have a cold start issue and BMW dealers would fit some extra loom in and a resistor. Not sure if yours will have this, but a knackered set of old plugs will not help at all.

[tetleysmooth]

Cheers Andy.

[Speedtouch]

NGK BPR6ES is best for M20B25s.

[tetleysmooth]

NGK BPR6ES is best for M20B25s.

Set of those tomorrow then.
Gotta admit I've used NGK's in a lot of my old bangers, and I've always found 'em ok.

[Speedtouch]

If you have cold start issues, it could be that the blue temperature sensor that screws into the back of the thermostat housing needs renewing; this instructs the ECU on the engine temperature and adjusts the mixture accordingly. It would also be worth checking the state of the distributor cap and rotor arm - I've owned BMWs that haven't had them changed in 20 years!

The ECU can be reset by disconnecting the battery for half an hour or so, but the correct starting procedure after doing this is to leave the engine idling for at least 10 minutes to let the base idle settings be relearnt, switch off, then go for a drive. I sell a chip which dramatically livens up this engine, giving better torque and improved mpg.

[tetleysmooth]

I changed the coolant temp sensor last Thursday. It's made things a bit better, but still got the 'splutter' on start up.
The battery I had on it was fubar, so it's got a brand new one on now.
The car was without a battery overnight, but I'll follow the procedure you explained.
Thanks.
p.s. Would your chip improve cold starting?

[Speedtouch]

I'd say ensure that the normal service items (spark plugs, rotor arm, etc.) are properly attended to first. A chip improves the driveability of this engine by removing flat spots in the standard program, but won't help with cold starting if there's an underlying fault. Please see my advert with other Zoner's Feedback http://www.e30zone.net/modules.php?name ... 72&start=0

[Andyboy]

I'd echo the comments about the cap and rotor. My 730i had an issue last year where it ran very poorly from cold - it still had the original 1989 cap and rotor which were absolutely shagged. Once warmed up it was okay but the first 2-3 miles were painful.

Air flow meters respond well to an internal clean up with ultra fine went and dry (1200 grit) and WD40 to clean up the surfaces the flap moves on.

[tetleysmooth]

Glad you said that about afm's Andy.
The one on the car is suspect, I have a spare, but I think it's been 'got at'.
Is there a basic setting for the mixture screw? i.e. If you screw it all the way in, how many turns should you turn it back out?
Getting a bit involved this thread, isn't it, but hopefully be of help to others too.
I've just been out and started the car, you could almost hear the plugs pick up one by one.
When it did warm up, the idle speed was wavering between about 6 - 700 rpm, not a steady idle speed as you would expect.