Idles at 1500rpm and always constant
 

As you read from my topic, my 1990 TT idles at 1500RPM. It started doing this on one Saturday night. The only thing I did with my Z Sat. night different from other nights was that I had injected some 104octane booster stuff and run my car hard for an extended amount of time. Anyways, about a week and a half after all this, and a couple new gas tanks full of gas, and my car is still constantly idling at 1500RPM exactly. Any ideas? The car used to run like that when cold then went down to around 800. Oh, and besides my 1500RPM idle, the car drives just fine. What gives?

Re: Idles at 1500rpm and always constant
 

octane booster can screw up your o2 sensors witch could cause a high idle. If you also noticed a change in gas mileage this is likely the problem.

Re: Idles at 1500rpm and always constant
 

I'm assuming that the VG30DE(TT) relies heavily on non-fouled O2 sensors to keep the air/fuel ratio Stoichiometric. My NA Z32 currently has a similar high idle problem but surprisingly I passed smog with a higher than normal idle speed (manual tranny). Also, aside from a high idle, during a cold start my rpms drop to about 900 while running very rough for appr. 2 minutes then smoothing out as the engine warms up.

Out of curiousity, how many miles can the average Z32 TT and NA go from a full tank of gas to less than 1/4 empty??

My shifting occurs at about 2500 rpm to 3000 depending on grade with a slow gradual build up of rpm (automatic transmission style shifts). The highest available octane in San Diego has dropped down to 91 which I constantly use.

My stock NA can get me no more than 200 miles with the needle on the Empty line.

How abnormal is this??

Do fouled O2 sensors read that lean of a reading to overcompensate fueling??

Thanks

donkayroo@hotmail.com

Re: Idles at 1500rpm and always constant
 

The only reason I pointed out the 02 sensors above is he said the high idel came soon after using octane booster. This stuff is terrible for emission controls and could easily damage the 02 sensors.

But for your ????s
Sounds like you have a thirst Z.
On my N/A I get from 270city-300hwy miles(304 my longest! 245miles my lowest). Ive heard of other N/As averaging slightly lower like around 260 city miles per tankful. On the TT I hear the ave is around 230-260 miles. Gas mileage depends highly on driving habits.

My driving habits includ shifting around 3500-4000rpm in 1st and 3k every gear thereafter. Hwy crusing averages around 2700-3500 rpm.

When O2 sensors are bad the ecu will recieve a reading of either the car running rich or lean. I had a talon that had the o2 sensor go out and the ecu was reading rich and leaned out my a/f mix. I was averaging 34-40mpg NO B.S. With a lean reading the ecu dumps fuel which can cause poor fuel mileage. You see the extreme of gas mileage I had above so the lean reading could also have exteme results.

I'm not sure about the smog test and how much your cats can clean out but i wouldn't think they could handle a 14mpg Z. It could also be your throttle position sensor having a bad reading causing you ecu to dump fuel. Or a leaky injector (if you smell fuel consider injector, if not ignore) On you cold idle some injectors that are going bad have the habit of running poorly when warming up but smooth out once warm. But if could also be one of the sensors i mentioned above.

The easy way to determine if it is a sensor it check the ecu for error codes. Check twinturbo.net under FAQ for instruction on how to do this.

Re: Idles at 1500rpm and always constant
 

Well, thanks for the help guys. I'll look into checking the O2 sensors and doing a diagnostic on the ECU. That's sounds like that probably is the problem. And wow, Dunkayroo, you get horrible gas mileage! I tend to get around 270-280 a tank!