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I'm posting this for a relitive with a '90 740 b230f .
The thing is now idling fine, but when just above idle, the rpms start surging like crazy up and down.
So far he's replaced just about everything sensor wise, AMM, idle valve ( it tested bad), speed sensor , tps , fpr, etc.
He's replacing the tank fuel pump now , and is almost at wits end. Not much left to replace aside from the ECU and ignition computer.
The car is about 1900 miles away, so I can't see it first hand.
Any thought here?
Thanks------Robert
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-------Robert, '93 940t, '90 240 wagon, '84 240 diesel (she's sick) , '80 245 diesel, '82 Mercedes 300SD
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posted by
someone claiming to be Atl780PRV
on
Thu Nov 18 09:50 CST 2004 [ RELATED]
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Same problem, except there was no down surge, only upwardly escalating surge. The culprit was a binding return spring inside the throttle/kickdown/cruise control pulley. Simple to replace if you can find one at a boneyard. Cost $3.50. Lube it (old one) up with a good penetrating oil first. That might do the trick. Test whether it is the pulley by turning it by hand all the way to full throttle then releasing it. If it sticks, even slightly, there is your problem. For those who aren't aware of what it looks like: It sits atop the intake. It looks like three small pulleys atacked atop one another with bare wires coming from it. These are the wires from the throttle, cruise control servo and transmission kickdown cable. If you can't find one at the junkyard, carefully dismantle the old one and observe where the spring(s) may have dislodged from the spring stops. Bend them (spring stops, not springs)back to their original shape and reinstall them. It will be obvious what I am talking about when you open up the pulleys. Not too difficult, just be careful to remember what came from where. Good luck.
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hi there,
I don't think the fule pumps r the problem... Check your hall sensor connected to the dist. hausing. by time plastic booth covers the terminas crackr or breaks and causes all kindas of that kind of problems.. If he has a broken plastic booth ( it was like that on my B230F engine.) order a replacement and change the booth.. but soon he will need a new hall sensor or a rebult dist which comes with nes shaft seals, hall sensor, rotor,dist cab.. my car runs fine at least a lot better than before. but it still surges sometimes.. it takes me where i wanna go and till i have the money to order the rebuilt dist. i am fine with that...
i hope this helps...
Sammy
p.s: After checking the hall sensor, check your fuel pump relay, radio sups. relay, ignition module.. u mention u already installed the new know sensor...
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I second changing the IAC, youll probly find your problem there, it may be working correctly at idle but just a tad above it is could be malfuncationing causing the issues you are having.
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It's new. The old one did test bad, but the new one didn't have a whole lot of effect it helped at idle, but did nothing for the off idle surge, I heard it over the phone and it was quite an rpm range span. and he did check the hoses and all other sources for possible vacuum leaks ( the guy is competent , and professionally trained ) This one is a real head scratcher.
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-------Robert, '93 940t, '90 240 wagon, '84 240 diesel (she's sick) , '80 245 diesel, '82 Mercedes 300SD
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I scratched my head and came up with a couple of WAGs. These thoughts are only offered because of the desparate tone of your message. Maybe they will trigger a thought or two for yourself or others.
Is it possible that the idle position switch is misadjusted, stuck on, or shorted? Theory being that the ECU thinks it is still on idle, and tries to adjust air mixture / idle speed.
Any idea if the timing is stable? (Faulty knock sensor? Dirty contacts on the connector?)
How about a 'jumpy' engine coolant temp sensor? (Broken wire, Shorting wire, Dirty contacts?) Have your friend hook up the LED test tool or Voltmeter to the CO test point to see if the voltage follows the surge cycle?
Check the throtte plate for play at the shaft. Confirm that the screws holding the plate to the shaft are secure. I have read that Carb cleaner is a more agressive solvent than throttle body cleaner and if it is used for cleaning the throttle body, the seals on this shaft can be damaged. (May damage throttle position switch also.)
Keep us up to date and please post the solution when found.
Dan
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Knock sensor new, contacts cleaned,coolant temp sensor new, Throttle position sensor new ( I was thinking bad TPS too, but it is new, probably wouldn't hurt to test it anyway ). I believe he did use carb cleaner on the throttle body, but before installing the new throttle position sensor, I'll have him check for leaks at the shaft on the throttle body, but I think he already did, I know he went over all the manifold gaskets hoses etc with some starter fluid, no idle changes anywhere.
Also it is a california model, but he already tried the disconnect the egr routine, no change
One other symptom:
It will idle ok, and he can stick it in gear and it will run down the road at idle, but if he tries to step on the gas, it will falter and stall
The really odd thing is that it was running fine, then he didn't drive it for a week, and then this.
Thanks----Robert
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-------Robert, '93 940t, '90 240 wagon, '84 240 diesel (she's sick) , '80 245 diesel, '82 Mercedes 300SD
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I was about to suggest you check that the TPS and IAC connectors have not been swapped by mistake (IAC connector to TPS and vice-versa), but you say this problem started on it's own after it was running fine. Check anyway. Refer to the wiring-diagrams for the car for identifying wires by color. You will need to scroll until you see your ECU model.
You could also start eliminating certain components: unplug the TPS at idle and see if the problem changes. When the car is idling fine, unplug the IAC and again see how this affects the running. As someone said earlier, also check the coolant-temp sensor (the sensor under the intake-manifold near cylinder 3). This is an important input to the ECU.
Noel
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posted by
someone claiming to be Al
on
Sat Oct 30 12:04 CST 2004 [ RELATED]
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Check the rubber hose that runs between the Turbo pipe just before throttle body and the idle control motor. It connects to the metal pipe at 6 oclock on the underside. If that hose has a hole or split it will cause the surging you describe.
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