BrickBoard Archives
The files contained in this listing have been automatically archived from the active forums. Because the vast majority of posts are now in one place, this archive is considered legacy. You should use the SEARCH feature OR choose your topic and select date tabs within the forum you choose.
Intermittent stalling / rpm surge[240-260/1987] posted by Brent Avery on
Monday, 27 April 1998, at 4:09 p.m.
An intermittent running problem has been occuring & I suspect it could be
the fuel pump relay. From what I've read & heard the relay usually just quits
but a friend's 1986 760 Turbo had the same symptoms - it would either stall
but start up immediately, or the engine RPM would suddenly surge to
between 2 - 2,500 and back down to idle then run normally or stall again.
This cycle would repeat itself and then disappear . I disconnected the
air mass meter when it was acting up and the problem went away- plug it
back in and the problem was back again. I did it once more and the
engine RPM increased,but not as dramatically. I've tried 3 different
relays ( all used & '87 vintage ) and only one worked well - for a while.
Could it possibly be a sensor ? I should mention that the AMM was
replaced 2 mos. ago. The relay is a double contact type & I gather
it is tied into the AMM & either the idle air valve or the throttle switch.
I disconnected the AMM while the engine was running ( found out that
it's a no-no ) since it still runs well except for this one problem I'm
hoping I didn't do any damage.
Re: Intermittent stalling / rpm surge[240-260/1987] posted by Dave Stevens on
Tuesday, 28 April 1998, at 4:31 p.m.
A misbehaving idle valve (actually idle air valve motor on an LH-Jet system) shouldn't put the rpm much over 1600. Tapping on the idle valve body or blipping the throttle will often cause the idle to return to normal if this is the problem. On the LH-Jet system, the idle air valve gets its signals from the ECU and is not connected to the fuel pump relay (as auxiliary air valves were in earlier K-Jet).
Quite right, disconnecting your AMM is safest done with the ignition off (arc induced voltage spike could fry sensitive ECU logic). The ECU detects this and puts itself into crude operating or "limp home" mode, ignoring many of the engine sensors. If that actually makes an improvement then the usual suspect is a faulty AMM, but in your case it's been replaced. Also, your symptoms sound like they go away once the engine is fully warmed up.
I would be more suspicious of the engine temp signal from the block (under #1 intake port), either the wiring (hopefully your year isn't affected by harness rot), the connector or the sensor itself. Try cleaning up the wiring and connections at the sensor. A voltage check at the ECU connector is the formal diagnosis here.
Hope those ideas help.