Contour Enthusiasts Group Archives Forums General Troubleshooting Low idle rpm & misfire at idle

Recently I have been experiencing low idle speed (400-500 rpm) & a misfire at idle in my 1996 2.0L ââ?¬Ë?Tour & in an attempt to solve the problem I have done all the standard things e.g. Clean MAF, IAC, Throttle Body etc. I have even had the Fuel Injector System cleaned & the problem still exists. I have a set of Magnecor Plug Wires accompanied with Motorcraft AYFS22FM Platinum Spark Plugs installed. It should be noted that the misfire only takes place at idle otherwise the car runs fine. I am at my wits end & therefore I am using this medium to solicit advice in solving this problem any & all comments/suggestions will be greatly appreciated.

How are the CATs ?


A realtime scan should tell you the problem if you can get one.

Check fuel pressure, if it's high at idle the FPR is bad or vacuum is not getting to it.
Check static timing.
Test the PCV system for crankcase vacuum.
Test for exhaust backpressure.

Rogerm60
Thanks for the input it's greatly appreciated. I have access to a OTC Genisys diagnostic tool & I have used it to do a real time scan & everything seems to be within specification. However, I intend to replace the PVC valve & will check the Fuel Pressure Regulator (FPR) but can you advise me on how to check the ignition in the static mode also how do you check the exhaust backpressure. Your response will be greatly appreciated.

The problem could still just be the IAC or the idle air bypass if so equipped. The engine would be more prone to missing at low RPM.


Use an inductive timing light to see if the same cylinder always misses, or if it's random.

Check engine vacuum at a steady normal idle speed for diagnosis. A steady 17-20 in. HG reading is normal.

If the system is in closed loop and the ECT, IAT, TPS and mixture look normal I would check these other things.

Check for exhaust backpressure by fitting a low pressure gage to the upstream DPFE port. Should stay under 3 PSI if the CATs are not clogged. This usually causes a loss of power at higher RPMs.

PCV system should cause a mixture problem. After a visual check, pull the PCV fresh air hose and fit a vacuum gage. Plug the intake side. Crankcase should pull down to around 8 in. HG or better. If not there is a crankcase leak or excessive bypass.

Static timing is cam timing. Pull the valve cover and verify slot position at rear of cams @ #1TDC.

Fuel pressure should raise to about 45 Psi at idle.

Do a compression test. A warped or sticking valve may be at fault.

I'm having all the same symtoms you are with my Zetec as well.
I've cleaned the IACand all emision sensors as well. Did a fuel system clean with my tech and checked for vacuum leaks. There are a number of people here with this problem. I have a post about this going right now.

Well folks I have fianally isolated my missing problem to my EGR system by doing the following. Last night I removed the vacuum line to the EGR valve & plugged the hose with a golf tee & this morning the car ran without skipping a beat. I have therefore concluded that my problem is due the EGR system i.e. some flow it taking place at idle & causing the misfire at idle. I am sure that it�s not the EGR value that�s causing the problem as it was recently changed & the misfire would continue if the EGR valve was defective. I later today reconnected the vacuum line & removed the electrical connector for the EGR Vacuum Regulator & again it ran like new. I am therefore convienced that it�s the EGR Back Pressure Transducer (DPFE) that's the cause of my problem. What I find strange is that at no time did I get a CEL, I intend to procure a replacement unit & will advise of the final outcome. However, anyone having the similar problem can try this method & see if it helps.

Good work!

This was covered most recently HERE.

The reason you did not get a P0402 was likely that EGR codes are dependant on info from the DPFE.