84 240 DL Acceleration Hesitation/Idle Problem

[seanlango]

Hi,

When accelerating from a stop or from below 10 mph, I experience a
hesitation just after the gas pedal is depressed. The engine stays
running, but cuts out almost entirely for 3 seconds or so, and then
picks back up again.

Also, the idle runs in an uneven way, high then low, over and over.
This sometimes evens out once the car has been running for a bit.

The following has been checked:

- throttle body cleaned out
- throttle switch cleaned and then carefully reset by a dealership
technician
- jetronic ECU leads tested system grounds and throttle switch
resistance checked out correctly
- gasoline sample checked for water -- gas is good
- replaced the blade fuse (25) that is near the ignition coil

I'll also mention that I replaced the entire throttle body/throttle
switch with one from my parts car which had been working just fine
before it was a parts car but has been sitting dormant for 2 years.
This replacement yielded the same hesitation, but with a slightly
higher idle, as that car had had in its running days (I figure this is
just where the idle adjustment screw was set).

The spark plugs were replaced 2 weeks ago when the car was stalling,
and I'm about to replace the wires, plugs, rotor/cap, air filter just
to take care of that all.

Does it seem like it could be the Idle Air Control Valve? Does anyone
know of any way to trouble shoot this? I have one in my parts car, if
necessary.

Also, does anyone know how to troubleshoot/listen for the fuel pumps
on the 240? I found info for the 700s online, about jumping terminals
on the fuel pump relay and then listening for the sound of the pumps,
but nothing for 240s.

Thanks for your help!

 

[Perry Noid]

so many possibilities, but give this a try:

with the engine OFF, disconnect the Air Mass Meter connector, then
re-connect it... do this 3 or 4 times to rub the contacts clean. Leave it
connected and start the engine. See if there is still the same hesitation.

I had a similar problem with my '89 240, and found that this would fix it. I
eventually made it a permanent fix by using a little contact
cleaner/conditioner on the connector, and by GENTLY bending the prongs in
the connector inward, so they made better contact.

Like you, I also replaced the throttle position switch (mine was actually
defective!), but never found that to make much of a difference....

 

[Perry Noid]

oops... hit the SEND button too soon! I also wanted to mention that a good
possibility is an air leak, causing the air/fuel mix to be too lean. Check
all the hoses to be sure they are connected at BOTH ends, and there are no
splits or holes that would suck air into the manifold.

 

[finnegan]

Hi,

When accelerating from a stop or from below 10 mph, I experience a
hesitation just after the gas pedal is depressed. The engine stays
running, but cuts out almost entirely for 3 seconds or so, and then
picks back up again.

Also, the idle runs in an uneven way, high then low, over and over.
This sometimes evens out once the car has been running for a bit.

The following has been checked:

- throttle body cleaned out
- throttle switch cleaned and then carefully reset by a dealership
technician
- jetronic ECU leads tested system grounds and throttle switch
resistance checked out correctly
- gasoline sample checked for water -- gas is good
- replaced the blade fuse (25) that is near the ignition coil

I'll also mention that I replaced the entire throttle body/throttle
switch with one from my parts car which had been working just fine
before it was a parts car but has been sitting dormant for 2 years.
This replacement yielded the same hesitation, but with a slightly
higher idle, as that car had had in its running days (I figure this is
just where the idle adjustment screw was set).

The spark plugs were replaced 2 weeks ago when the car was stalling,
and I'm about to replace the wires, plugs, rotor/cap, air filter just
to take care of that all.

Does it seem like it could be the Idle Air Control Valve? Does anyone
know of any way to trouble shoot this? I have one in my parts car, if
necessary.

Also, does anyone know how to troubleshoot/listen for the fuel pumps
on the 240? I found info for the 700s online, about jumping terminals
on the fuel pump relay and then listening for the sound of the pumps,
but nothing for 240s.

Thanks for your help!

Sounds like a vacuum- air leak.