Too basic for help? rough 320i

[Ukhozi]

1987 320i automatic,

I have scanned the forums, YouTube and Google for an answer and although some ideas popped up, no definitive answer because 1, State side they don't know this car and 2. Europe far and few about and it always ends up recommendations to check the Idle control Valve and throttle position sensor but the L-jetronic doesn't have them, very basic, thank heaven.

She used to idle with a sweet buzz from the tailpipe now it is heavy, uneven and pulsing. seems to rev OK, despite the shot pedal bushes etc but definitely rough and probably not great on the motorways although kicking down produces a good burst of speed as required, If it wasn't for the diaphrame device it would stall.

The fact the diaphrame control works is surly a sign that the vacuum is good.

I have adjusted the air screw thingy on the back of the inlet manifold above the valve cover and fitted new vacuum tubes and a new valve cover to inlet breather hose, even a new valve cover cap,, checked all 6 plugs and leads.

Dizzy is down below not on end of cam by the way.

I can't see any loose wires, spare connections or loose pipes.

So, any pre-'89 guys up to speed on the old M20B20 lump?

[Speedtouch]

Check out the Zone Wiki:
https://www.e30zone.net/e30wiki/index.p ... e=Jetronic

I would also carry out a thorough check on your ignition system, cylinder compressions and valve ('rocker/tappet') clearances, prior to fiddling with the injection system.

[BristolE30]

I’ve got this issue on my 325i and have searched high and low for the issue, testing and replacing many parts.

Try disconnecting the battery and resetting ecu. Does it get better for a short while? Mine does so I’m thinking the ecu is suspect. Either that or a very elusive vac leak as I’ve down multiple smoke tests

[Ukhozi]

The L-Tronix doesn't have an ECU as such, only on the later post '89 motronix, see what I mean about being early and basic.

As for the vac, the diaphrame woks well as does the brake servo which are connected to the vac system so don't think it's that

Seems the diaphrame does what it is supposed to. pushes out on low vac thereby opening the throttle and stopping the engine from stalling and staying back when throttle is opened, (increasing vac).

It's a basic anti stall device in other words. So after warming up and setting idle speed on the stop, with engine off set stop to nearly touch arm. certainly more reliable that electronics for sure.

[flybynite]

The L-Tronix doesn't have an ECU as such, only on the later post '89 motronix, see what I mean about being early and basic.

The L-Jetronic fitted to my 1983 certainly had an ECU. The E30 L-Jetronic (more accurately the LE-Jetronic was the first to have an ECU

A small vacuum leak on one of the smaller pipes, or on the inlet boot will not greatly affect the likes of the servo but will sure as hell affect the running

It is not really the vacuum loss that causes the problem it is introducing air at the wrong place that does

I have spent many a happy day chasing vacuum leaks on leaky Jetronic pipes. A passtime I'm not keen to repeat