Hi,

1990 Volvo 240, 205K miles. As the subject says, the car sometimes stumbles/hesitates when I acclerate hard from a stop. It almost seems like it's bogging down a bit. If I acclerate more, the rpms do not increase..the car barely moves forward. When this happens, I take my foot off the acclerator and then glenty push it and it then is OK. In the past 5K miles I've done the following

new Bosch AMM (warm air hose disconnected)
fuel filter
wires and cap (Bougicord, Bosch). Did not do spark plugs yet
air filter
cleaned throttle body
filled up tranny fluid, 1.5 quarts low.
waterproof fuse in engine bay
spun fuses (did not retension yet)

This issue happens when the car warm or cold. It idles great and drives wonderful once I'm crusing along. Like I said, it's a random issue that happens when I acclerate from a stop. I'm not braking hard, just normal braking.Maybe vacuum leak?? Coil? Power stage?

Just hoping someone can help me out with this issue. Car still has a random stumble/hesitation when I acclerate from a stop. A gentle release and then push of the acclerator seems to help get the car rolling. No codes, CEL, etc...Car runs great when its crusing down the road. I'm guessing it must be a vaccum leak somewhere? I did inspect the accordian hose after the AMM for holes. AMM replaced 5K miles ago w/ Bosch.

Which of the many ideas suggested here did you try... or the things in your original post that you said you had not yet done, did you do. We know two things you checked/tried.

So how is the paste on the ignition amplifier
What do the spark plugs look like that you have not changed
How did the fuse box service including the retensioning and cleaning the fuse holders go
How does the wire to the CPS look (not sure if this one was mentioned)

0 resistance on plug wire sounded a bit off as a cause but I was willing to go with it when you said it was solved.

It is unlikely to be the cause if the stumble is consistent, but have you swapped in your known good fuel pump relay or resodlered the new one?

Have you tried to read the diagnostic codes? It is possible that there are codes stored in memory even if there is no CEL.
--
1966 122s, 1968 142s, 1969 144s, 1979 245dl, 1989 244gl

I checked for codes, nothing but 1-1-1. I took off the hose between the intake and AMM...no cracks. There was a bit of oil coating the inside though...enough so that when I held it up vertical, some dripped out. Flame trap is OK. Throttle bottle cleaned about 5K miles ago. Any idea what I should do next? Spark plugs could be a bit old? Maybe I should unplug the computer a few times to clean up that connection?



Thanks

Very similar drivability symptoms on my 240 were cured by finding and repairing a split in the "accordion" intake duct between the AMM and the throttle body. The split was at the bottom of a fold and hard to see. I wrapped it with vinyl electrical tape until I could obtain a new duct.

When I tried to accelerate, the engine would rock slightly on those soft motor mounts and this apparently would open the split up, leak a lot of air that was not being seen by the AMM and give a huge lean stumble. At a steady RPM with light throttle, the symptoms were largely gone.

So check for an air leak there or possibly in other hoses/tubing.
--
Bob: Son's XC70, daughter's 940, my 81 and 83 240's, 89 745 (V8) and S90. Also '77 MGB and some old motorcycles

Well, I spoke too soon. After 30 miles of driving, the original issue is back. The car is very sluggish accelerating from a stop (not all the time though). A gentle release of the petal and then gentle acceleration seems to 'fix' the issue. I'll check the accordion hose after the AMM to see if there are any small holes. Happens when the car is cold, hot, dry, wet, etc... All randomly though. Could possibly the pickup tube in the tranny be slightly clogged? If it was the O2 sensor, would the CEL come on? Car idles great, drives great once it's moving.

Turns out it was a bad spark plug wire. They tested one of the wires and it had zero resitance which was causing the misfire. These were new Bougicord wires with only 1,000 miles on them from IPD!!

Car runs great now.

Isn't it how it works. With new wires, who could have guessed a defective part! Me, when it comes to Champion spark plugs too!

Phil

So today the car has a very bad idle. It doesn't stall, but the rpms are much lower than normal. Now whenever I accelerate, it seems like it has a bad miss. I think it smells like it's running rich. Maybe O2 sensor? No CEL. Didn't see any vacuum leaks. I limped it to the local indie mechanic as wife wants to be certain problem is fixed when she drives it. Will post with what happens.

Possibly the ignition amplifier. It causes stumble and hesitation problems.
--
1980 245 Canadian B21A with SU carb, M46 trans, 3:31 dif, in Brampton, Ont.

If you are using Bosch platinum plugs it is time to change them. If you can not see that tiny piece of platinum down in the porcelain, they are done.

Another thing to check out is the rotor button if it has been in there a long time or has been used with platinum plugs. Just a theory of my on that when the plugs get worn out the voltage builds up in the rotor button and blows out the resistor inside the button. It could be just a coincidence but it has happen twice to me.

Others have mentioned not liking platinum and the rotor buttons, as simple as they are, go bad!

Ignition wires get blamed a lot but moisture brings out their worse side. Does it have to be rainy for this to happen?

I mark it this symptom up to random misfires and you lifting the foot changes the misfire conditions. The throttle plate is the slowest moving part under the hood. The computer is a lot faster but can over adjust when it all starts with mixtures burns changing on two out of four cylinders. Actually, one being worse than the occasional other cylinder, really blows the computers communication map into a "stuttering mode" of which it does not exist.

Of course, "All" of these oberservations may have only happen to me in a dream and some have said, in what I smoked today.....(:).... I do not think they meant ham or fish either!

Phil

Did you clean the idle air control valve and all the vacuum fittings on the throttle body and manifold?
Dan