Cross reference that AMM (or MAF) with your Bosch LH-Jetronic version.

http://www.nuceng.ca/bill/volvo/database/ecu.htm

The Bosch LH-Jetronic version 2.4 and 3.1 on 240 came with the little black LED box.

As your is an 1988, if an early 1988 you may have the Bosch LH-Jet 2.2, no black box, and the distributor-mounted Hall-effect sensor for timing (or is that 2.0?) yet with either a test light or a multimeter, you can reference stored fault codes in the LH-Jetronic ECU and the EZK ignition ECU. You can search the brickboard for these procedures. Uncle Art B may have some article threads on here that'll help in the current article set of the brickboard archive. Uncle Art's post are massively helpful.

You may want to check ground, connectors, continuity through the wire harness; certainly in the engine compartment and into the connector harness on the two (LH-Jet and EZK) ignition boxes.

Help using http://www.volvowiringdiagrams.com/

I'll guess you have your big blue Bentley Volvo bible for Volvo 240 or at least some service manual? Even the Haynes (Brown color cover, 1997 final edition print) is better than nothing.

Yet for beginning your diagnosis (in no order):
- Look at the easily accessible wear items like cap and rotor, spark plug condition and gap, air filter. Those radio suppression relays (you may have only one) may be a cause).
- Visually inspect the same old same auld like wiring connectors to things like the two coolant sensors, connector to the throttle position switch. Inspect the main fuel pump(s) relay or try one known to be good and delicious. If you find cracked solder welds on the main PC board, re-flow solder.
- Unless upgraded and / or moved, you have the silly, open air, 25 AMP blade fuse mounted on a flat bar along the North America driver side inner-fender. The white plastic holder should have, long ago, been replaced with something better and sealed from the weather. I have seen these fuel injection system fuse holders on the 1990 and owlder 240 LH-Jetronic equipped make contact with ground and fry some wires with spectacular results. If that fuse has been sittin' there in that North Carolina or U.S. East Coast weather, I'll bet you have some corrosion there or at any place along any engine compartment wire harness connector. (You may want to inspect the whole wire harness through your awesome, if fabulous 1988 240 estate [wagon - 245].) (You may want to look at the state of the fuel sender on top of the fuel tank (check for rust up there, yet do not remove), yet you have to lift up the cargo area floor board to get access to the grey galvanized steel plate at some time, yet well beyond you issue here.)
- You have two coolant sensors. How old is the coolant? One coolant sensor is used by the engine control system and may go wonky, yet not often in a way to interfere with the engine warm-up cycle, unless it is failed. (Mix coolant using antifreeze and deionized, distilled, or demineralized water. NEVER use tapwater in engine coolant.)
- Maybe have a go and the wire harness grounds through out the wire harness. A loosen and re-tighten works. Better with a little grease yet be careful of over-torque. If you find broken ground spade or lug connectors that cannot reconnect, replace them using a crimp.
- You have two points where the fuel injectors ground to the engine. These are the ring lug connectors secured on the #2 and #3 runners under the M6 bolt. I think, or read, or recall something about someone suggesting flowing solder into the where the wire is crimped into the connector. Maybe a Volvo TSB on this? You do this to optimize the ground for the injectors.

As you and other discuss the AMM (or MAF), be certain you disconnect the silver preheat intake hose from the exhaust manifold pre-heater plate and shroud. The works in the air filter box that closes the flap valve when it is warm out fails always to the hot, so remove it or stuff it up if NC-state performs a visual inspection of emission control systems. If hot air crosses the AMM (or MAF) in (i hate hot) Summertime, you'll fry that AMM (or MAF).

Have you checked that the fuel rail fuel pressure regulator (FPR) with the vacuum hose at one end is not leaking fuel through the vacuum hose and into the engine? But you'll check this when you closely inspect all air intake systems components and vacuum lines, yes?

Sorry this is not in some sort of order, but your symptoms may be caused by any host of causes in the electrics, air intake system, sensors used by engine control (LH-Jet, EZK), vacuum leaks, and more.

Take a look-see at the 700-900 FAQ here at https://www.brickboard.com/FAQ/700-900/ for symptoms you describe.

Hope that helps.

Sundae MacDuff.
--

While some folks may not agree with how I executed this diagnosis, I do believe it to be correct nonetheless.

So, I also have a 1990 Saab 900, which also uses a Bosch LH Jetronic injection system. The AMM from the Saab swaps right into the Volvo, albeit the Saab uses LH 2.4 whereas the Volvo uses the 2.2 system. Otherwise the Saab and Volvo have similar engine displacement, at 2.1 and 2.3 liters respectively. The Saab is a 16 valve and should flow a similar amount of air to the Volvo's 2.3, or so I reason. I momentarily fretted the difference in injection systems, but hoped the differences wouldn't be so great as to blur the information I was getting from the car.

Anyhow, the swap has yielded results, and I believe the AMM has been the source of the running woes.

The LH 2.2 ECU is not convinced it has found its soul mate in the 2.4 air meter, but they get along well enough to let the car run smoothly. Acceleration is not as snappy as it would be with the proper AMM, but the hesitation is gone and the idle is smoother than it has been the last couple months. Now, being a sunny day here means I cannot confirm the resolution of rain related concerns, but being an optimist, I have faith they will disappear as well.

Problems during damp or moist conditions generally make me think of cap, rotor and or plug wires.

You do need several spare parts for trouble shooting and one is definitely an AMM. I had a couple fail or at least start to fail causing intermittent hesitations, swap in a known good one and the problem goes away.

Dan

I had to read over the symptoms several times to try and come up with a commonality.

This one you have here is tough when trying to pin it with such an inter mix of intermittent issues.

I want to go with your gut feeling of the AMM going out of calibration too.
Guts are at the center of our bodies, are usually very reliable at their job, until something else gets thrown into that it cannot deal with.
The AMM maybe in the same situation.

I assume you have check for corrosion inside the connector to it and checked the accordion hose for cracks, loose clamps and bad auxiliary hoses.

My thoughts with this was a variance in air volume beyond its control but you then lean on it and it sounds like it was blowing itself clear of a rich mixture.
Opposite of lean or the lack of it raising fuel pressure?
Could the FPR be malfunctioning?
Sometimes working rich or lean making the fight jump to the oxygen sensor and having it "jousting" with the ECU to correct the issue? It's always self tuning.

I read over it again,
"Stumbles a bit when cold, and even after stumbling has passed their is a mild lack of power."
"When warm, acceleration feels "normal", although it will occasionally hesitate or lack a bit of power."

Its then the ECT slips into my mind as maybe its out of calibration for the engine temperature environment but there is nothing to point it out for sure except you phrases.
All these variances, with just enough questions left to wish I was there, but doubting the whole time it would help!

NowI read again that there is "Rain" during the gremlin parade! Oh boy, this is a Saturday mystery movie. I am getting into the armchair now!

With that one scenario, I jump to ignitions wires or the coil wire in particular, But the cap and rotor are kissing cousins too!
Could it be that easy? So basic?

I felt myself doing the Tom Hanks head shake in front of the computer, when he was trying to think of what to write in the movie "You Got Mail."

Well that's where is where I am! I thought up one plausible idea of it being an intermittent in-tank fuel pump. You mentioned the noisy main pump and I have say to myself..... "Self, ..... You have clues but not one good answer."

The "not good answer" is start with the basics and blame electronics last.

Sorry, I will just have to watch the thread and learn more!

Phil

a dying air mass meter is surely something to look at and also a dying oxygen sensor.



recently i had cause to repair a 93 sedan which had lacked power for over a year. idled poorly and simply would not accelerate worth crap. the owners replaced too many parts to list quickly with no effect. it also ran hotter than normal according to the gauge

ultimately the problem turned out to be the oxygen sensor wires had disconnected in the harness to the firewall. not saying thats your problem only that a faulty o2 sensor can cause all manner of troubles.