Hello all,

I've got a 97 f150 w 4.6 and 5 spd. that's acting up again. Recently, I replaced the spark plugs and must have messed some stuff up as the idle has become quite erratic. As I slow to a stop, I can feel the engine continuing to race and it will gradually slow after I push in the clutch to stop. At cold start-up, the engine will catch and race quite high before slowing down after several minutes.

I have already replaced the IAC, DPFE, fuel filter.

Any ideas on what to do next?

thanks

 

Could be a bad TPS. (Throttle position sensor)

 

Sounds like it's still trying to get warm or your MAF senor isn't working or has came lose.

 

Well,

I shot down the MAF with electrical contact cleaner to see if that would help and went out for a ride. Same problem. except, as I rolled up to a stop light, I pushed in the clutch, the engine kept on reving and I pulled a "cel" #1506 having to do with idle air contol over limit.

I just changed the IAC 2 weeks ago. any thoughts?

thanks

 

Surging is a symptom of a lean idle. The 1506 does NOT indicate a problem with the IAC. It simply says that the idle is higher than the IAC can control. The IAC will keep closing until fully closed to control the high idle. If it does and the idle is still high, and the throttle is closed, it will set the 1506. Air is getting into the engine somewhere, the usual suspects:

1. Vacuum leak
2. Dirty throttle plate/body
3. Idle air controller isn't closing

Vacuum leak is the most likely. In fact, the PCV tube elbow behind the throttle body is the most likely vacuum leak. It causes a high idle and a lean idle (the surging).

The dirty throttle plate/body is modestly likely but if the TPS isn't very near closed, the 1506 won't set. It can learn the newer throttle position if it sticks slightly open. A down side of this theory is it wouldn't make the mixture leaner, so no surging.

Finally, the IAC. You've replaced it and it wouldn't be lean.

I'd guess the odds are 70% vacuum leak, 15% dirty throttle body, and 15% IAC.

 

Hello all,

I went out and removed the hose from the PVC valve that feeds into the throttle body. The foam insulation had deteriorated at the corner but it was still air tight.

I guess the next step is to open up the throttle body to see if there are any obstructions and spray down the butterfly plate. Is there any adjustment that I could try on the TPS?

thanks

ihilani

 

Well, here's the latest status report.

Today, I sprayed down the throttle body to make sure it's clean. I also started the motor up and while experiencing the high idle, unplugged the IAC. The idle immediately fell to normal.

I removed the IAC and took a look inside and saw that the rubber plug was not pluggin the hole. So I took the assembly back to NAPA and they compared it with their only other IAC and it had a larger gap. It was also missing the spring. The parts guy looked at the code on the shelf part and noted that it was the same part number with an "a" following.

Well, I took the springless part and tried it out and still have the delayed return to a normal idle.

any suggestions?

Thanks in advance for all your help.