Help idle & hesitation problem
 

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....

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)

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

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

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)

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

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

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