Here's the scenario - wife's 93 240 had been getting worse and worse at idling, no matter what the temp was. So I finally got some time, took out the throttle body and cleaned it up with TB solvent spray, blew air through vacuum line ports in the throttle body, adjusted throttle position switch to get click when butterfly closes, etc. Car started and idled just fine for a few weeks, then began having issues again. I took off all vacuum lines, cleaned throttle body again, removed intake manifold and cleaned, replaced oil separator on block, replaced injector seals, replaced flame trap, took out idle air control valve and checked for proper function, reassembled everything. Car is extremely difficult to start when cold and requires non-stop pumping of accelerator and 2500-3500 rpms to keep running. After perhaps one minute of that treatment, the problem disappears completely and the car runs great. WTF is going on? This car does not have a cold start valve under the manifold, only the idle air control. Any ideas? Oh, forgot to mention, swapped out AMM with bone yard spare and with another AMM from our other 93 240. With any of those three AMMs, the car behaves the same. Runs GREAT after a minute of nursing from cold.

To get people in to see the new 90s, my dealer sent out a coupon for one hour's troubleshooting - they did the same last fall also.

You might check with a dealer to see if they have the same offer.

HI,

If I'm reading this right, this starting problem is more prominent when the engine is dead cold and I gather, it has sit overnight or for a long period?


You said, the car is extremely hard to start and you have to do a lot of pumping of the pedal to keep it running at the upper RPM's. Like a "whole lot" above any idle point.

Well, first of all pumping the pedal is not helping anything. It will only confuse the computer programming because of throttle switch jumping open and closed. It's the communication idle or run or what you want the engine to do.
The pedal does not pump gas or air it is just an air vane.

What I surmise that is happening is it lacks fuel pressure or a filled up fuel rail. An empty or low on volume fuel rail takes time to fill.
It most likely has drained over night.
Either back to the tank or into the engine.

Have you tried, turning the key to start and back off "several" times, but NOT actually crank the engine over. You should hear the main pump only "hum" and quit.

This will run the pump(s) for a second or so, as to pre-fill the fuel rail and its components on the line.
If it starts and goes better after trying this technique, then you are on to something!

Also! Listen, for the pumps to be running, for a second after you stop cranking the engine.
You want to know, if the pumps are actually "kicked on" and were running while you were cranking.

Just in case there is a bad or a delay in the fueling system relay area.


It is the easiest way for gasoline to go back to the tank, is by the fuel return line from the fuel pressure regulator, that is mounted on the fuel rail.
It can leak back through a check valve in it. FPR's do fail more often than the pressure side of pump related parts.


You do not say anywhere if it ever smells like the engine is rich or flooded.
So, I will again surmise, that gas went to the tank, directly or back through the fuel pumps, if there is a bad check valve on the outlet of the main pump. This is rare, but?

It can also leak out of an injector, usually meaning one, since there are four, but even this is rare thing I have found to be an occurrence.

If so,
The oil in the engine will eventually smell of gas dilution going on.
Smell your dip stick oil from a paper towel or sniff over the valve cover cap.
Keep the engine off on that one, unless, you have chapped lips! (:|)


Another thing around to put "the sniff on" is the vacuum hose to the FRP.
If the rubber diaphragm inside is leaking out some raw gas, it will get sucked into the intake manifold and cause a temporary rich condition. The engine will buck to try to burn that off.
Similar to a that stuck cold start injector idea you mentioned, that you don't have.

Of course this would lead to a serious leak there and the car would run rich all day long.
Very bad gas mileage might be and was not noted. So, I bet not.



I need to ask does this happen more often or not if the tank is less than half full or full.
There is a feed pump in the fuel tank that can starve the main pump, of which, can make it harder to start but more likely all the time.
It's a far fetch for the morning or cold moment of sickness.

I would not even go down the AMM route since the car runs great otherwise.

The coolant temperature sensor can alway be suspect but it takes quite some time for an engine to warmup. It would run lean and display poor power until its warmed up.

That is, After warming up, to about halfway between cold and normal on the gauge so it can run on that mixture.
You say, it appears to go away rather quickly.
I think....
It's Hard to start, coughs and sputters for about 10 to 15 seconds for the whole ordeal.

I hope this give you some points to zero in on.
You wrote a very good description of what your car was doing, so I tried to do you one even.

Good luck and hope to hear you found something.
Phil

Thanks for the ideas. I was pumping on the understanding that rapid full movement of throttle results in ECU lengthening injection interval, simulating accelerator pump of old carburetors, but I may be mistaken about that being part of ECU programming. After going back through everything again, I finally went back to square one. Only issue was dead cold start. After just a bid of warming up, it would start just fine, run just fine, plenty of power. Gotta be either ECU or temp sensor. Needed another ECU for our other car so I went ahead and ordered it from FCP. No help. Pulled the intake manifold off and again and replaced the engine temp sensor, even though there's no way the engine could warm up enough in a minute or less to run properly. Well, guess what? That was it. New engine temp sensor and the thing is running perfectly. All of my intuition tells me the engine can't warm up that quickly, but I suppose it's only the temp of the combustion chamber that we're really worried about, not whether we can feel any heat emanating from the engine head or block. I definitely learned some new things with this problem. Thanks everyone for the help.

I recently had a problem with an 89 240 with similar symptoms. The AMM was the fault with mine. Do all the connectors in the plug look to be in good condition?

Does the behavior change with unplugging the AMM and trying to start it cold?

I would guess that the 93's have a coolant sensor that keeps the ECU supplied with the current engine temperature. You can check its function at the plug on the ECU. The resistance values are in the FAQ's.

I checked mine for being in specs when cold and then replaced the connector and started the car. I ran it up to operating temperature before shutting it off and once again pulling the plug at the ECU. Putting the meter back to the correct connectors allowed me to check the resistance at operating temperatures and then monitor the change as the temperature fell.

As long as you have a digital meter handy you can check the voltage fluctuation of the O2 sensor while the car is running. Again the procedure is in the FAQ's

Randy

Turned out to be the engine coolant temp sensor but that diagnostic intimidated me - I was in too big a hurry to DO SOMETHING to think about how simple it really is to check. My bad. Replacement of the temp sensor has the engine starting perfectly.

Some of the things I would check are the idle air control valve, crank position sensor, fuel pumps and their relay, fuel pressure regulator and the O2 sensor. May want to give the coil, wires and distributor cap and rotor a look.
Did you read OBD codes?