a couple months ago my 2002 4.0L starting acting like it had a bad IAC .... dropping RPM"S at idle ... I had this happen to it once before ... it would idle fine then drop 100 rpm or so and back smooth ..... I cleaned it before and then cleared it up ... then it started again .... cleaned it and no help .... so I took it to a garage and he cleaned the MAF and IAC too ... then when I got it back it was idling different ... it was like it was loading up and surging ... so I take it back and he changes the fuel filter and spark plugs and said I had the wrong plugs in it ... they were too short and he puts in Autolites .... and he raised the idle ..... but it still was idling bad... so I put a new IAC in and still no help .... then I get some bosch plus's and put in (same as I had in it before and it ran fine for 25,000 miles) still no help ...... running out of ideas ... it has 112,000 miles ... gas mileage seems fine .... just ruff at idle .....

so does anyne have any idea's as where to look next ? Thanks

 

v8 swap maybe! lol. jk. that sucks though.

 

the autolite plat. done the same thing so plugs are not the problem .... wires maybe ........

 

I put motorcraft plugs in today and it's still not right .... dug a little more and and the PVC was pretty much plugged ... renewed that and itstill doesn't idle right ...... Help


PS it's a damp rainy night and I started it up in the dark and I'm not seeing any sparks anywhere

 

check for vaccum leaks.

 

when he said he raised the idle, what exactly did he mean? idle is computer controlled on your truck.. its not like he can just change it..

 

it was the EGR vacuum regulator that was bad .... changed that and it idles as smooth as a baby's bottom ...

 

try looking for a vacuum leak in the upper intake. mine has done it for months and i cant find anything wrong. the feul trims are way high though. mine is a 99 with 214,00

 

problem was solved