another (different?) hot start problem

[guinness]

My M42 (in an E36 318iS) has started to act up.

First it started perfectly when cold. But hot starts needed a few well-timed taps to the accelerator, otherwise the revs will come come down and the car will stall. Once the revs stopped bouncing, the car will be fine. And the car drives fine.

Now on cold starts, the revs bounce a little (once? twice) after starting, but won't stall. However, on hot starts, I can't get the car to idle unless I rev it hard (past 2 to 3K rpm), then the idle will stabilise. Car still drives fine after that.

Struggling to figure out the stomp test - can't seem to get the "5 stomps in 5 seconds" on the accelerator right. Ignition should be in the position where all the lights come on (and the ABS and Airbag lights go off after a few seconds)?

Where are typical vacuum hose crack/break points that could lead to such a problem?

Fuel pressure regulator or O2 sensor? I can get about 500km on a full tank.

Any help appreciated! Thanks!!

[roundel318]

I was doing a stomp test the other day with the TPS disconnected, it didn't work then.
Perhaps something is up with your TPS?

[guinness]

I was doing a stomp test the other day with the TPS disconnected, it didn't work then.
Perhaps something is up with your TPS?

what is the impact of a bad TPS on normal driving? Like is said earlier, once the car settles down and struggles past the initial hot start, the car drives fine - and will idle fine.

[guinness]

After some troubleshooting it looks like the fuel pressure regulator could be the culprit.

When I disconnect the vacuum hose to it, I can start fine on warm starts. When connected, it will give me the hard warm start problem.

What does the vacuum hose to the fuel pressure regulator actually do? Is it all right to run without it plugged into the fuel pressure regulator?

I don't seem to have any fuel leaking from it - but I guess a new FPR is in order?

What happens on M42s when the vacuum hose is connected to the FPR, and when the hose is not?

[Deftones]

the fpr regulates the pressure in the fuel rail, as the manifold vacuum increases, the fuel pressure in the rail is increased too. this is done for providing sufficient fuel to the injectors at all rpms, because higher the rpm are, more fuel is injected and lower the pressure will get in the rail. so if you have problems with it maybe your car runs too much rich and cannot start, when you disconnect it the pressure falls and the fuel injected is nearly correct

[roundel318]

If it's fine after a bit with idle, it looks like your FPR might be the direction to look?

[Home made iS]

i know im trying to revive an old thread but i have this exact same issue, have had for 12 months or so now.....really shitting me.
k Ive replaced and or had professionally cleaned...
F.P.R
injectors
one way valve on fuel pump (local euro mechanic advised that the one way valve in the pump tends to fail)
fuel pump
currently doing the cam chain tensioner as it rattles like a coffee grinder atm.
plugs, leads etc
checked the alternator in case of low charge.

After all this I am still at a loss as to what could be causing the issue.
its a converted e36 m42 into 90 e30 318i (originally m40) everything else is pretty much standard

[Home made iS]

Update: Sorted the issue, seemed to be idle air bypass(mixture at idle) screw was way out of adjustment due to originally being on an m40.
now it starts hot, cold or in the otherwise, no stutters, farts or hiccups, everytime.

Not saying that this is everybody's issue, but it worked for me. :cool:

[DesktopDave]

Good to know, thanks for the update.  I've never fiddled with the idle air bypass screw.  IIRC, on the US models (catalyzed) it's plugged and might even be absent.

There is also a connection in the main engine wiring loom (the bit across the firewall) for non-cat models.  Unplugged for catalyzed; plugged in for non-catalyzed.