After highway driving the car stalls when foot is taken off the gas.

Tiny
SHAKER340
  • MEMBER
  • 1993 DODGE DYNASTY
  • 3.3L
  • 6 CYL
  • FWD
  • AUTOMATIC
  • 172,000 MILES
After highway-speed driving the car stalls on the exit ramp as soon as foot is off the gas pedal. Check gauges light comes on. Oil pressure goes to zero. Car starts back up but the RPMs need to be kept up to keep engine running. Around town in short distances the car seems to run fine, no stalling, good idle. Has good battery, new gas filter, new PCV, new EGR valve. Today I got the car home and tried to restart it while engine was still warm, it didn't want to start. Pumped gas pedal a couple times, it started- then I had to keep the RPMs up to keep it running. Please advise. Thanks.
Thursday, May 1st, 2014 AT 9:42 AM

15 Replies

Tiny
HMAC300
  • MECHANIC
  • 48,601 POSTS
Scan fr codes and check fuel pressure with a gauge autoparts rent it. Shold be 46-48 psi w/vacuum hose connected to regulator and 55 without
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Thursday, May 1st, 2014 AT 10:03 AM
Tiny
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Haven't had a chance to follow up on your suggestion yet but in checking further I found a 15 inch section of wires in sheathing that had broken off completely and tangled around the axel. The two wires are black with a thin blue stripe and dark green with a thin orange stripe. I appears that this section was connected originally to a line off the power steering pump? The car has had no steering issue. I've been looking all thru my repair manual to try to identify this in case it is a sensor that is affecting the stalling. Any idea what those color wires are used for? Thanks.
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Thursday, May 1st, 2014 AT 12:33 PM
Tiny
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Found the color of the one wire is Dk Blue with orange, not green as I first thought. The manual says it belongs to the power steering pressure switch. Would this affect the stalling? What does the power steering pressure switch do? Do I need to repair/replace it? Thanks
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Thursday, May 1st, 2014 AT 12:41 PM
Tiny
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There is a dark blue with orange that runs off the power steering pump switch on one side and the black with blue line goes to other side of switch but it also goes to the coolant temp, throttle body etc. So fix that first it may solve your problem.
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Thursday, May 1st, 2014 AT 12:42 PM
Tiny
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Yes you will need to fix it but you will have to see where it tied in to begin with. The power steering switch raises idle when you go to lock on the steering but because other switches are connected that has to be fixed as well.
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Thursday, May 1st, 2014 AT 12:44 PM
Tiny
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Made a connector, spliced the broken wires to the computer on one end and repaired and connected the connector end going to the power steering pressure switch. Now the car still doesn't idle well. Engine runs rough. Is there anything that needs to be "re-set" I don't dare drive it as it will keep stalling. HELP! Thanks.
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Monday, May 5th, 2014 AT 1:56 PM
Tiny
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Do what I said in first reply also check for a vacuum leak.
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Monday, May 5th, 2014 AT 3:06 PM
Tiny
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No fault codes now (Had #25 & #52 before changing 02 sensor) Fuel pressure 50#. No vacuum leaks found. Replaced idle control motor, 02 sensor, cleaned the throttle body with carburetor cleaner as it was varnished up. When I disconnect any vacuum line from the intake manifold the RPMS increase. The car is running rich. When I stop the car with the brake it idles so slow the voltage drops to 12v on the gauge and the car quits. If the car is in neutral it idles, but a little rough. The engine runs great if the rpms are up. What do you suggest at this point?
Thanks.
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Monday, May 19th, 2014 AT 9:30 AM
Tiny
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Check compression also have you fixed th broken wires yet? And are they soldered or just twisted together. Like I said in first replay fix the whole harness first then check things out it can have an effect on engine running. Also make sure battery is in good condition including load test autoparts do for free and have clean terminal ends as well as a tight belt for alternator.
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Monday, May 19th, 2014 AT 9:43 AM
Tiny
SHAKER340
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I have completed all your previous suggestions. The car is idling better, but still idles down close to stalling when I stop and add vacuum load by applying the brakes. The RPM's recover, but very slow. Can I manually adjust the RPM's at the throttle body without causing a problem? What should the RPM's be? How do I connect a Tach/Dwell meter to an electronic ignition car? The car seems to idle better after I get it out on the highway for a while. Is it possible that the computer is retraining?
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Sunday, June 8th, 2014 AT 11:49 AM
Tiny
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You can't set the idle the computer does but try cleaning throttle plate on both sides and iac hole with choke cleaner they get gummy and do what you are talking about.
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Sunday, June 8th, 2014 AT 3:42 PM
Tiny
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Thank you for the response. I have already removed and cleaned the throttle body and all the ports and chambers. I replaced the IACM, tested the throttle position sensor, temperature sensor, coil pack, fuel filter, PCV valve, EGR valve, O2 sensor, plug wires and spark plugs. I changed any suspect vacuum hoses. How can I check to see, how low the RPM's are dropping? What should the idle RPM's be? Thank you.
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Sunday, June 8th, 2014 AT 5:52 PM
Tiny
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What's the fuel pressure like I asked many replies ago
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Monday, June 9th, 2014 AT 6:33 AM
Tiny
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Fuel pressure is 50 lbs.
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Monday, June 9th, 2014 AT 7:58 AM
Tiny
HMAC300
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All I can tell you is torescan for codes now that the wiring is fixed and car is running straight. You can check vacuum at idle and normally a scanner wil pick up what the rpm is. If vacuumis 15' or below check for clogged exhaust. You can also check compression see if you migh thave a head gasket problem. Or have cooling system pressure checked as well. Other than that I'm out of ideas and have no further suggestions.
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Monday, June 9th, 2014 AT 9:32 AM

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