Idling Hard

[pulsar57]

Hello. Recently (although I think it's been doing this for a little longer), my 1991 TT has been idling rather hard, it's especially bad when I turn the car on in the morning after not having driven it for awhile. It's generally idling at around 500 rpm, but sometimes it will drop even lower. I've actually stalled it a few times backing out because I have to go so slow due to having a slanted driveway. It's seemed to be idling pretty hard when coasting around turns and stuff as well. The car seemed a little sluggish driving it today, but it may just be my imagination, it's kind of hard to tell for sure.

Regardless does anyone else's Z idle like this? It has 100,000 miles on it by the way. Is it just showing it's age, or is there something I should have checked out?

[RED_DET]

Hard idle on cold start should be around 1000-1100 rpm and should drop down to 750. 500 is way to low for any idle speed. Check TPS for correct voltage spec and also adjust base idle. I would look for vacuum leaks as well.

[pulsar57]

Hard idle on cold start should be around 1000-1100 rpm and should drop down to 750. 500 is way to low for any idle speed. Check TPS for correct voltage spec and also adjust base idle. I would look for vacuum leaks as well.

Thanks for the response. I'm probably going to have this checked out. I was wondering if the rpm was low, it seemed pretty low to me, but I wasn't sure.

[t.mcginley.jr]

Could just be a sticky IACV, the valve tends to get gummed up or stuck over time. Could also be carbon buildup on the throttle bodies, bad coolant temp sensor, etc. Idle at 750 in gear is the golden number, but it can vary up or down ~50 or so rpm depending on temp. Like RED_DET said 500 is way too low.

[marcyprojects]

Curious to see where this goes. My 90 has what I would call a hard idle compared to all the other cars i own/have owned. Checked everything that was mentioned here, ECU reads code 55 all clear but I still have a slight vibration felt under the seat. Car runs beautiful, all the power is there. I was thinking maybe motor mounts but my better judgement tells me its unlikely.

[ShiroZ32]

Also make sure your injectors are 100%. Mine was idling just like yours is and it turned out that injector #1 wasn't playing nice. New style injectors and connectors switched in and its all smooth now.

[marcyprojects]

tru. I do have an injector that has a connector that looks kind of suspect. ill probably just go ahead and replace that. Weird still because if the injector was out completely, I feel like there would be a considerable loss of power somewhere which I havent seen.

[DCaff300ZX]

Definitely check your injector connectors for green corrosion, common and will cause idle issues as will a failing injector.
Also, the IACV unit on the DS rear of engine has two connectors that have the same issue, and can cause idle issues as will the IACV itself if it gets gummed up as mentioned.
Other connectors of the same type as the injectors have the same corrosion issues, an afternoon under the hood cleaning all visible connectors is time well spent.

[pulsar57]

Still have not got this checked out yet, although it's on my list. I'm trying to compile a list of all the things that I want to have checked out when I take the car in. I've noticed (although perhaps its just my imagination) that sometimes I when starting the car from a stop (light, stopsign, etc), and I get on the throttle, the car seems to not rev up immediately, but hesitates if it were. Although other times it doesn't do this. Not being sluggish, it just seems that sometimes the car requires more gas than others to get it started. It's quite possible that this is just something I'm imagining though.

[Bearcat112]

I have a 92 Nissan Sentra SE-R and injector #1 is not firing. Not all components are installed in the car because it is a Bandit race car. I put a test light in the back of the ECU harness pin #101 and the test light does not light but does for the other 3 injectors. I turn the knob on the ECU for test Mode 1 and the lights flash 13 (Engine coolant temperature (ECT) sensor range/performance problem) and 34 (Knock sensor (KS) -circuit malfunction). These seem strange codes to stop an injector from firing? I also ran a wire directly from the ECU harness to the positive on the injector and grounded the negative directly and still can not get the injector to fire? Tried different ECU and that did not resolve the issue.

[ThisIsSparTTa]

Injectors are fired by the ECU connecting the circuit to ground, not to positive. Be careful with what you're doing.