Hello everyone! I've searched around the forums a bit and couldn't really find an answer so I'm going some of you can help me figure this out.

I have a 1990 240DL, 230,000, standard transmission and I love her dearly. However, she's been a little difficult lately.
The idle is a bit low and rough and seems like it wants to stall (but hasn't yet) and when I give it too much throttle too quickly, she chokes up and jerks until I ease off a bit. If I completely floor it, there's power loss and the car slows down until I once again ease off the gas. I've also noticed that when shifting gear and switching off between the clutch and gas pedal, it sounds like it's missing. Just one single 'poof', but its there. It seems to be missing a little during acceleration too but I can't really hear it.
I checked the trouble codes (CEL is on) and got 1-2-1 and 1-3-1. The maf was just replaced a couple months ago and didn't seem to fix the problem. The car also has new distributor cap, rotor, and wires as of a year and a half ago.
Also, with code 1-3-1 which is "RPM sensor to EZK missing", it doesn't match the given symptoms which is the engine not starting. The car runs fine otherwise, and as long as the acceleration isn't too fierce I've had no other problems. However I want to fix it so it's not constantly in limp home mode!

I did just recently noticed that it has a small exhaust leak further down the pipe before the muffler, but I couldn't detect one close enough to the engine where I think that could be the problem. I used to have a Hyundai that exhibited the same problems as the 240 so I replaced plugs and wires and distributor, which helped slightly, but it turns out there was a hole in the flex pipe causing the loss of power and misfiring. Do you think the exhaust could still be the problem? I'm at a loss.

Edit: I forgot to mention, when I have the key in the 'II' position, I can hear one of the fuel pumps turn on, and it stays on. Is this normal? If I'm under the hood, I can hear it near the fuel pressure regulator. However, there doesn't seem to be any leaking of any sort. I thought maybe the pre-pump could be one of the suspects in the hesitation.

"Also, with code 1-3-1 which is "RPM sensor to EZK missing", it doesn't match the given symptoms which is the engine not starting."

• 1-3-1 does match the no-start symptoms perfectly. When the EZK fails to get RPM sensor pulses, the engine will not start. Or, if it does get started, it may quit or mis-fire intermittently due to engine vibration or torque reaction when accelerating.

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Start-Run Sequence LH 2.4

1) During starter cranking, the Crank Position Sensor (CPS) sends timing pulses to the Ignition Control Unit (ICU).

2-a) The ICU sends these CPS pulses to the Power Stage (aka Ignition Amplifier), to initiate spark voltage pulses from the coil.

2-b) At the same time, the ICU also propagates these CPS-based pulses to the Fuel ECU to allow FI operation (no ICU pulses means no FI operation).

3-a) The Fuel Injection "System"* relay (previously energized at Key On) sends 12V power to the:
• Fuel Injection ECU,
• Fuel (pump) relay coil + side (ECU controls coil ground)
• Idle Air Control valve (IAC) (ECU controls coil ground)

* The System relay is in the white case with the Fuel pump relay.

3-b) When FI ECU receives (CPS based) ICU pulses, it "energizes" the Fuel pump relay by grounding the relay coil (– side).

At this point, the engine runs until the Ignition is switched off, which in turn shuts down the FI system.

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Bruce Young, '93 940-NA (current), 240s (one V8), 140s, 122s, since '63.

My guess would be to much air or not enough fuel.

A bad Fuel Pressure Regulator can cause acceleration problems. Not enough fuel pressure for good atomization. Too much fuel could be returning to the tank. It can cause starting problems if the at rest volume is not held overnight in the fuel rail.

Too much air behind the AMM can spell big trouble. A lot more issue with having more of this or that happening at different times.

Starting with the accordion hose for being loose or having cracks. Inspect with a light from the inside.

Another, is a serious intake gasket leak. If its got a lot of miles they have been know to fail.

They start out out as rough idle or a shaky idling motor. When the really start leaking it will almost stall because it will be all that the Idle Air Control motor can do to shift against it.
If IAC not fairly new or dirty, well you guessed it! A stalling or flopping to run or stop. Again uncontrolled air.

Until you rule out excess air entering, swapping parts is an expensive way to no solution! IMHO

Phil

I forgot to mention that the fuel pressure regulator and accordion hose were both replaced a few months ago. I have yet to check the IAC, but the throttle body was filthy. Now that it's clean the idle had evened out, but it's still misfiring when I shift gears and acceleration isn't too great unless I steadily increase pressure to the pedal.
Today though I noticed the noise from the fuel pump is sounding a bit erratic and not the constant hum it usually is.

Remove the accordion ducting from the AMM to the throttle body and carefully inspect it for splits or cracks, especially in the bottom of the folds. That was the cause of my similar symptoms. I repaired it with vinyl electrical tape until I got a replacement about a year later. If this is the cause of your problem it's a temporary free fix.

The replacement unit from one of our popular mail order suppliers was notably much thinner plastic than the factory original, and the stub for attaching the Idle Air Valve hose broke off. I pulled a couple of good ones from 240's in the JY - much more substantial.
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Bob: Son's XC70, my 83 240, 89 745 (V8) and XC60. Also '77 MGB and some old motorcycles

Thanks for the suggestion, I forgot to mention that the accordion hose was replaced at the same time as the MAF; dealer part. I did clean the throttle body which was filthy and now it's not pulling 1-3-1 code and the idle is normal. Acceleration is still funny if I give it too much gas.

clogged air filter, clogged exhaust as the symptoms sound like a breathing problem. When was the last time you cleaned the throttle body as this will effect idle and throttle response. Pull the vaccum line off the fuel pressure regulator and smell for gas. You can jump fuses with paper clip and listen for both pumps to activate.

So last night I replaced the air filter(it was dirty, but only moderately) and cleaned out the throttle body which was FILTHY. also replaced the throttle body gasket. I forgot to mention in the original post that the fuel pressure regulator and lines as well as accordion hose to throttle were all replaced a few months ago. Still need to check the fuel pumps, but Im starting to suspect one of them is bad because the sound of the pump is becoming a bit erratic and not a steady hum.