I have a 95 chevy blazer with 194000 miles on it. My question is, would the IAC cause bad MPG? It has a new FPR, fuel filterand fuel pump. It will run great when you first start up and drive, but after awhile it falls on its face. Most of the time you cant get up past 35 MPHafter it falls on its faceand when in park you can not rev up the moter. If you turn it off and start it back up it will run fine for awhile and then fall on its face again. I think it may be the IAC. Thanks for any help and guidence.

 

The IAC won't affect performance off idle by much, if at all. I would look more at the fuel supply, oxygen sensor output, and the ignition (spark) system. If heat has a role in this, then it is possible that the ICM (ignition control module) is overheating.

Also, do not overlook the possibility of a clogged cat. A little bit of cool down time with a partially clogged catalytic converter can cause it to act ok after you have shut the engine off and try to restart. A clogged cat would definitely limit the RPM the engine can achieve.

 

Thanks swartlkk, oh and sorry for the slow reply. I went ahead and knocked all the honeycomb out of the cat to see if I would have any problems and I have not. Then I thought I would Sea foam the heck out of the moter before I put a new cat on. The fam and I took it on a long trip this weekend and did not have any problems with the old girl. My MPG went from 14.5 to almost 21. I think I will replace the IAC and The TPS just for the heck of it to see what the old girl will do. One more thing,with all the honeycomb knocked out of the cat should it set of the check engine light because it has not. Thanksforyour help and excellent advise. Bluecoot

 

While I would agree that the performance of a gutted cat would be better than that of a restricted and/or otherwise failing cat, you are not as efficient as you could be with either a functioning cat or a straight pipe. Sooner or later, with a hollowed out cat or straight pipe, it should trip a code for catalyst efficiency or something to that effect.

Federal law requires your vehicle to have a functioning catalytic converter even if you do not have inspections that check for it. The fines are pretty steep.