I did a search but haven't read a post w/symptoms that my car has. Car starts and runs fine in the morning, but after it's warmed up it develops a low surging idle and hesitation on acceleration. Some times it's so bad it'll stall the car. Car will restart, but only after some difficulty. Things I've changed (for new parts) previously for idle problems in the past. 2001 Rotors Cap Spark Plugs Wires 2002 OVP 2003 alternator Found a loose vacum hose 2004 Nothing 2005 fuel pump fuel filter temperature sensor injectors cleaned spark plugs ignition coil ...new idle problem this year is frustrating me. I've already spent appprox $500. I'd hate to continue to throw parts at it randomly. What should I try next? Oxygen sensor? (Has anyone tried the Ford replacement?) Fuel pressure regulator? MAS? ICV? Please help....

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JR
1986 Gold 300E 4Dr automatic

Not sure on your model but on my 380SE I had bad ignition control module. Car felt like it was "missing" on take off and also stalled a couple of times. Unfortunately this is about a $300 part(rebuilt)

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95 E420 ( 76K) SOLD
85 380SE(125k)
95 SL500(72k)

Well, a worn airflow meter potentiometer will cause problems at idle and off-idle acceleration, if performance is pretty normal once you get the rpms up. Reason is, this is the range where the wiper spends most of the time, and the element wears thru. If you disconnect the pot's plug, and idle steadies out, this is the problem. Part available from Bosch (check past threads) or with the whole airflow meter from MB sources, if you're rich.

Steve

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'91 MB 190E 2.3
'08 RAV4 Ltd 3.5
'83 Lazy Daze m'home 5.7

I would pull the icv valve...and give it a good cleaning with brake cleaner....better yet, if you can let it soak overnight.

wouldn't cost you more than a couple of bucks.... watch for brittle hoses connecting the icv

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1989 300ce 129k
( facelifted front,updated tail lights, lowered suspension,bilstein sports, lorinser front spoiler, MOMO steering wheel, remus exhaust,stainless steel brake lines). (Gone)

1997 s320 154k (what a ride)

1994 e320 Cabriolet 98k (finally)



1972 280se 4.5 153k Owned for 12 yrs, sorry I sold it


[/SIGPIC]

hmmm...so you guys don't think it's the O2 sensor or the fuel pressure regulator?

I think I'll try:
1. Cleaning out the ICV (no cost...except brake cleaner, hopefully relatively easy to RR)

2. then I'll replace the airflow meter potentiometer ($80). I did a search and found the thread. I'm not too familiar with setting the .7V using a voltimeter (sbourg, can you explain that portion to me in "lay mans terms". Please give me "idiot free" step by step instructions on how to attach and read the meter. Pics would be great!)

3. If that doesn't work, I'll change the O2 sensor ($40 Ford replacement)

4. igniton module (Ouch....$300??!!! Hopefully I don't get this far)

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JR
1986 Gold 300E 4Dr automatic

Pull the passenger side front carpet and check the O2 sensor connection.

Good luck,

Regarding the air flow potentiometer: try
http://www.europartsdirect.com/
They sell it for 45$.

Good luck, Bruno

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1992 300TE 160 kmiles

If you plan to remove the ICV, first buy all the rubber in the vicinity. At the age of your car replacing it all would be wise anyway due to hardening and cracking, and it is unlikely to survive the disassembly process. Not an expensive deal, but a lot of trouble identifying all the right pieces. Phil at Fastlane worked with me to via e-mailed pics and parts diagrams to get all the parts. I also replaced the rubber bottom of the airflow meter plenum for good measure.

Much easier is testing pot function, since the plug is easy to pop off with the air cleaner removed. Replacing the pot means popping out the screw covers, then carefully scribing on the airflow meter body so the new one goes in exactly the same orientation (mounting allows it to rotate for calibration). This should allow you to start up. Replace the pot carefully - the wiper assembly is delicate and stays attached to the airflow meter assembly. Once warmed up, probe and measure from the center pin to ground at normal idle. Near 0.7V is fine, but allow to stabilize a minute or so after each adjust.

A good pot has little effect on steady-state. It provides acceleration enrichment as its main function. The erratic idle occurs because erratic contact fools the ECU that you're wildly thrashing the accelerator. Inputs from the pot, the O2 sensor, and outputs to the EHA and ICV end up playing a wild fandango. Then when you actually want to accelerate off idle, the pot fails to deliver the enrichment message in a timely fashion.

Steve

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'91 MB 190E 2.3
'08 RAV4 Ltd 3.5
'83 Lazy Daze m'home 5.7

Bruno_300TE

Thanks for the link. I ordered it today. $63.51 w/5 day shipping to Hawaii. I'll work on it next weekend after it comes in.

LarryBible

I'm still debating on whether or not to change the O2 sensor too. I'll change the MAS potentiometer first.

This new surging idle & hesitation problem is frustrating ...it's has to be something simple (sensor/relay) because at around 1500-2000rpm the car runs like a champ. Ahhggggg. I knew spending nothing on the car for repairs in 2004 was too good to be true. 2005 is making up for it. I've already spent over $500 on this problem the past 2 months.

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JR
1986 Gold 300E 4Dr automatic