High Idle, Low MPG's.........Help?

[tdaggett]

Got a '99 Sr5 3.4 Auto 4x4, e-locker 193000 miles,a while back for my son.
So far, we've done the usual oil and filter change, new plugs, belts, tranny drain and fill, new air filter, and still the idle is high. Around 1000-1100 at start up and sometimes up to 1200-1300 after it gets warm.
No smoke out the pipe, runs really smooth, and the tranny shifts like butter, it just idles high, and the MPG's are down to around 12-13 (I think largely due to the high idle) He's got 265/75/16's on the stock wheels. Those aren't much larger than stock, so I dont think they're affecting the mileage that much.
Any suggestions, recommendations, or experience here? Vacuum maybe? Help?
Thanks
Travis

 

[Sig220]

One easy/cheap thing to check is to clean your intake. Process is almost like changing your plugs on the passenger side. Remove piping to the intake and when you look in it you will see a "flapper" a oval metal damper that opens as you open the throttle..........it will be blackish/dirty spray with a good carb cleaner or intake cleaner with rags to catch the runoff and dont forget to clean the edges.

It builds up carbon allowing more air in then necessary which is balanced by more fuel and increases your idle speed.

Good Luck!!

 

[JeremyH]

Vacuum leak somewhere. Most likely on the intake.

Getting a CEL?

 

[tdaggett]

Cleaned the throttle body, MAF sensor, Throttle pos sensor and it's even higher now. Any more suggestions? Idling around 1300 right now. Where to begin with the vacuum? Any time I unkook any vacuum line, the idle goes sky high. The only time we get a CEL is when I unhook something. Hook up the line again, and we can reset the CEL. May have to go somewhere and check any stored codes?
This thing had an Injen CAI on it when we bought it, and I don't like the look of the vacuum hoses, or the way it howls through the intake. We have a Volant intake with a box on it coming this week. Does changing the intake require any adjustment somewhere else?

 

[brian2sun]

Could be you just need to reset the ECU after cleaning the TB by pulling the neg. terminal of the battery for about 45 minutes. Also, the IAC is the main thing in that TB cluster that affects the idle the most, but it sounds like you didn't clean that so that could be your problem. You may need to go back and do it again because when you clean the TB, but not the IAC, you're essentially "dirtying" the IAC even more because the gunk from the TB will run into the IAC and clog it worse.

If all this doesn't help, you could try the coolant temp sensor which is like a <$30 part and has an effect on the idle also. Test the TPS, make sure the butterfly on the TB isn't bent or staying partially open. And it could also be as simple as the throttle cable going from the pedal to the TB is too tight, there should be a little slack in it at rest.

BTW, the idle should always be around 1200-1500 at start up (when it's cold) and then it should settle to 700-750 once it's warm.

 

[tdaggett]

Could be you just need to reset the ECU after cleaning the TB by pulling the neg. terminal of the battery for about 45 minutes. Also, the IAC is the main thing in that TB cluster that affects the idle the most, but it sounds like you didn't clean that so that could be your problem. You may need to go back and do it again because when you clean the TB, but not the IAC, you're essentially "dirtying" the IAC even more because the gunk from the TB will run into the IAC and clog it worse.

If all this doesn't help, you could try the coolant temp sensor which is like a <$30 part and has an effect on the idle also. Test the TPS, make sure the butterfly on the TB isn't bent or staying partially open. And it could also be as simple as the throttle cable going from the pedal to the TB is too tight, there should be a little slack in it at rest.

BTW, the idle should always be around 1200-1500 at start up (when it's cold) and then it should settle to 700-750 once it's warm.

IAC? Thats new to me. What/Wher is that? If I can clean that, we'll unhook the battery and go that route.
Thanks for the input so far.
Travis

 

[brian2sun]

IAC? Thats new to me. What/Wher is that? If I can clean that, we'll unhook the battery and go that route.
Thanks for the input so far.
Travis

Re: 3.4L V6 Hard Start "hot" Cleaned IAC (Pics) - YotaTech Forums

 

[JeremyH]

Cleaned the throttle body, MAF sensor, Throttle pos sensor and it's even higher now. Any more suggestions? Idling around 1300 right now. Where to begin with the vacuum? Any time I unkook any vacuum line, the idle goes sky high.

That's exactly what it should do....

IMO, the best way to find a vacuum leak is to get a bottle of carb cleaner (or anything else that is highly combustible), install the tiny red spray nozzle and start spraying different areas around the intake. The engine should rev higher when you spray the area where the leak is located.

My guess would be somewhere between the intake manifold gasket and the leading edge of the throttle body...