when you idle the engine at 1500 rpm the idle goes up and down. when you drive at 1500 rpm the engine stumbles and misses, with a dead spot. i have replaced the following- EGR valve,EGR pressure sensor,hoses,fuel pressure regulator,spark plugs,coil packs,pcv valve,cleaned the throtel body,replaced air filter.before i did this their was a code P0401,no code now.and before i replaced all these parts, the problem would come and go. now its always their.i used to be a chevy man,im trying to expand. signed heavy chevy.
engine runs rough at 1500 rpm. on 1997 Ford Expedition
idle air sensor is bad
this engine has no idle air sensor. it has a new IAC valve, the problem is the EGR is opening to soon. cruising around 1000 to 1500 the egr opens and closes causing a surging effect , a stumbling. the idle goes up and down even in park. when you put it in 4x4 low you cant maintain a steady speed because of the surging the rpm is between 1000 and 1500 if any one has the fix i would be very happy, i have spent over 1500 dollars trying to fix this . you would be surprised''' my phone# is 706 237 3864 i will cut a jig for you.
Did you ever find out what was causing this condition? I have a 98 Expy 4x4 and it's doing EXACTLY the same thing for the last four years. I have also chased it down to the EGR valve premeturely/excessively opening at the 1500 rpm point. After a quick internet search for answers, it appears we're not the only ones and that this is not an uncommon problem. After metering out voltages and replaceing the EGR DPS and EGR valve, I have come to the conclusion that the computer is commanding the EGR control valve to cycle and open up the EGR valve...I'm just not sure why. So, now I'm going after any culprits that could be giving the computer bad feedback information. I'm thinking it could be bad O2 sensors although they aren't popping any codes...but they've never been replaced and I think 128K miles and 15 years is well past their lifespan. Would love to know if you found the smoking gun on this mystery. Thanks and hope you're still available on this 4 year old problem.
It sounds similar to an exhaust restriction.put a vacuum gauge on a vacuum line and rap the throttle while in park.the vacuum should snap back to what it was at idle.if it moves slowly to the reading at idle you have a restriction.also the baro pid is a telltale sign(if you have a scan tool available)anything in the 149hz and below is also an indicator.or if you have access to a backpressure gauge,should not read above 3psi.good luck!