Thanks for all the help so far guys. This has been the most frustrating problem I've ever had with my 1992 240. Here's a quick summary of the original problem, steps I've taken, and current condition of the vehicle.

1. Original Problem: Car would idle terribly at start-up. The problem seemed worse when the gas tank was near empty. The car stalled a few times and threw a check engine light and codes about the fuel being too rich/too lean and something with a fuel injector fault.

2. Steps Taken: I did find a problem with the air intake hose where one of the nipples had broken off on the back side that connects to the flame trap. So I have a new one in there now.

I also checked the vacuum hoses and replaced some of them.

The poor idle and engine shake was still happening so I went ahead and replaced the original in-tank pump since the vehicle has almost 200,000 miles and the problem seemed worse when the tank was low.

Unfortunately the engine shake still occurred and the idle was still poor after the in-tank pump was installed. I checked the operation of the pump using Art's method by removing the fuse and jumping the left vs right sides to activate the in-tank pump and external fuel pump independently.

I have checked and verfied that spark comes through the spark plug wires on all cylinders.

I have searched for vacuum leaks at the throttle body and cleaned the throttle body.

Last night I replaced the original oxygen sensor with a Bosch unit. The idle seems a little less erratic and the engine shakes a little less, but it still isn't smooth and it still seems like it is missing sometimes.

The fuel pressure regulator does not have gasoline leaking out of it when I remove the vacuum hose from there.

Current Condition: Car is driveable, but idles poorly at start up. The engine shakes some like it is missing or stalling. Not bucking as much as it was before the oxygen sensor, but still not acting quite right. When I leave my parking spot, the vehicle sounds like some sort of old fashioned car that is running really slow and erratic. Kinda almost like those funny cars at idle at the starting line before a drag race. It could be my imagination, but it seems like the exhaust smells of gasoline.

There was a suggestion for me to check the individual spark plugs. I can easily pull them, but I'm not sure what to check for.

Thanks for reading my long post.

Did I mention that Chad Henne stinks?

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Thanks so much guys. Especially Art and JWalker and whoever else was helping me out. You guys rock!!!

It was a combination of problems.

The main problem.

Spark plug #3 was bad. The ceramic stuff around the tip inside the engine was half gone. This was the cause of the misfire, lack of power, and I guess the gas smell coming from the exhaust.

The minor problem.

Several of the intake manifold bolts were pretty loose. So I tightened them up.

All is good with the world again with steady idle with no engine shake.

I'm tired. Hopefully I can go fishing this weekend instead of working on the car.

Tom

There was a suggestion for me to check the individual spark plugs. I can easily pull them, but I'm not sure what to check for.

Hi Tom,

That was a good suggestion. Kept thinking it myself until at the bottom, there it was.

Take a look at each of the four for color. Don't just look at them, smell them and feel for wetness. Most repair manuals have a generic color plate showing how plugs look under various conditions. As I wrote that, I flipped through a few of mine to find an example, but none popped up in either Haynes or Bentley. To find one, I had to look in one of those Chilton's some of us say they line their birdcages with.

Alternately, you can post a photo here.

I did not know the tank pump was being replaced for this symptom. Did you replace a working pump, or was the old one dead like most are? That quick test, with the paper clip, only checks the pump operates. It doesn't confirm the pump is actually moving fuel in the right direction, as you may have read about from my experiences. Have you swapped AMM's?
--
Art Benstein near Baltimore

Did you know that dolphins are so smart that within a few weeks of captivity, they can train people to stand on the very edge of the pool and throw them fish?

Thanks Art. I'll take a look at the spark plugs tonight after work.

Honestly I have no idea if the pump is pumping in the right direction. It does buzz to life when jumped though, but really no clue if it is sending fuel correctly.

The old pump was probably working fine. It might still be in the garage trash can.

I don't have a spare AMM to swap in.

As always Art, thanks for your help.

Tom

Base on the engine shake symptom, I would suspect the intake manifold gasket. Several bad ones have been reported here over time, and I have had one myself. It affected the #2 cylinder and looked (strangely) like it had been blown outward, rather than sucked in.

One cylinder being excessively lean will cause the shake. The O2 sensor will report the lean condition to the ECU, which will try to compensate by enriching the mixture. Maybe enough to set a 232 code, possibly others.

The plugs might indicate this condition if one is relatively cleaner (less sooty) than the other three. But I would just go for the gasket, given 200,000 miles.

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

Now, I'm more convinced your pump isn't the problem. If you didn't have to replace the sender, where the reversing problem stems from, it is highly doubtful the pump is pumping backward. Even with mine doing that (before realizing it) the main pump, with 275K on it, had enough suction to overcome the backward tank pump until the tank got low and the fuel got warm.

You've probably seen my oft repeated advice to have a spare AMM before you need one, because there's no sure-fire way of eliminating it as the culprit except to replace it with a known working one. And of course, how will you know the one you might pick up (no returns allowed) at Crazy Ray's is any good unless you've been able to check it out in a well-running car. Even so, you can find one in the BB classifieds or similar for not that much more than CR's gets for one, and perhaps know the seller has checked it in a car.

I expect your plugs will be sooty. Was the old oxygen sensor sooty? Contrary to intuition expressed by some, an intake manifold leak can make the car run rich, when the computer tries to compensate for it on the non-leaking runners. You'll see this on the plugs where one is not a sooty as the rest.


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Art Benstein near Baltimore

A bank is a place that will lend you money, if you can prove that you don’t need it.

Yes, I'd say the oxygen sensor that I removed had some soot looking stuff on it. Nothing thick caked on, but sort of a dull gray color to it. I replaced all the upper end gaskets when I did my head gasket back in 2009. More fun to look into tonight!

Good. No soot. Not a sooty!

Probably your plugs will reflect the same, and maybe that odor you detect isn't excess fuel, but the stink of lean burning. How's the temp gauge - any tendency toward overheating? You must be hyper-aware of that since doing a head gasket.

Did you pull the AMM's accordion hose and look for holes? Connections to it tight? Does the car idle better with the AMM disconnected from its electrical plug? Assuming you've already made sure the FPR vacuum hose has no gas in it, does the idle improve if you pull that hose off of the regulator and cover the end of the hose with your finger? Things to check, maybe before going to the effort of pulling plugs...
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Art Benstein near Baltimore

To steal ideas from one person is plagiarism. To steal from many is research.

Art,

The air intake hose that ran from the AMM to the throttle body had a sheared off nipple on the back side where it connects to the flame trap. I replaced that with a new hose from IPD. So that was one legitimate problem corrected.

Temp gauge is fine. I did the bypass a few years ago and all seems normal there.

Yup, pulled the vacuum hose off the fuel pressure regulator. No gas inside.

When the AMM is unplugged the car runs worse.

I'll report back this evening after I check a few things out.

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On my 1990 240, the problem you describe, including trouble codes,
has nearly every time been caused by small holes in the exhaust downpipe
around the lower bend and before the cat. Seriously. It was the last place I suspected.
Causes air/fuel metering issues big time.