Idle Question

[Salacak]

I just came from motor vehicle and they told me that my idle is not correct (I said no way it is accurate and working fine) but their machine shows idle is 2500 my gage shows 1300 and I think they were right. Car runs fine and idle looks normal but after motor vehicle experience I start watching closly and looks like my gage shows lower than actual numbers.

What can cause this and how to fix it.

Thank you guys for your help.

[backwoods lex]

Wouldn't you hear it if the idle were at 2500rpm? On my ES, anything near 3K would be growling. It should be quiet at idle.

[Shadow]

Idle @ 2500rpm? My LS cruise at 75mph+ at that rpm.

[Salacak]

They were testing the car and he told me come to between 2000 to 2500 there we realized my gage was showing 1200 when actually it was 2500.

[nc211]

Salacak, tell me this; when you put the car into gear, what does it feel like? If you're really at that high idle, then your car would SLAM into gear and you would have NO DOUBT something was wrong. I'm sorry, but I'm just not buyin' your mechanic's recommendation. I think you would know it right away if that were true, you'd have bashed up bumpers from flying into whatever was in front of you when you put it in gear. Heck, even 1,200 is too high unless you're car is cold and you've just started it. It'll hoover around that mark for 45 seconds or so, then start to slowly come back down to normal 600 rpm speed.

They were testing the car and he told me come to between 2000 to 2500 there we realized my gage was showing 1200 when actually it was 2500.

[Salacak]

No, no. This is the thing, car runs perfect and when it is on D idle shows around 0.2 or 0.3 driving nice, at the traffic light shows around same 0.3 (Kind of low but) this is the thing; I never notice something was wrong until at the motor vehicle guy told me to go up on idle up to 2500 RPM when I was doing so my idle was showing 1200 or 1300 RPM but his machines already was up to 2500 and he told me your RPM doesn't show correct numbers I said really and starding to realize that my idle shows low numbers. But I can not tell only idle shows wrong number or really car runs on a very low RPM. I don't notice anything wrong or any problem whatsoever. If only my idle shows wrong number, how can I fix that or if car really runs on very low idle how to fix that?

Thanks again guys you are the best.

[Shadow]

Salacak,

The gauge signal for RPM is independent of speed signal so collect some graph points with RPM vs. speed in highest gear (>50mph) for comparisons to other 1st gen LS to see approximately how much your gauge is out of whack. Post your data I'll compare with my LS.

[Salacak]

I was doing 50 mph and RPM was around 1000

I feel like it is low numbers but car runs fine and I have no trouble at all, it is not like at the stops runs low and stalls or anything; and also it is not feels like car engine runs high RPM and my gage doesn't show it either.

[nc211]

50 mph at 1,000 rpm's??

Hmmmm...this is getting interesting.

Oh master Bicol-ini, are you around ole' wise one?

[Salacak]

I hope someone can figure this out

[Salacak]

Anyone can help on this

[ylekiot1]

I think you might have a sensor sending the wrong information. I was looking at the shop manuals last night for a TPS issue and remember skimming across a sensor relating to RPMs. I think it also mentioned if it was bad that some codes would be triggered. Is the check engine light on? I'll post this evening and let you know what I find. I hope I am not off my rocker here.

[Salacak]

Thank you for reply, no check engine light or any other code comes on. I feel like you saying some sensor but no codes or check engine light comes on. I also start reading stuff and saw throutle clean up might help idle and power issues with the car but I don't know I can do it or not (I looked at tutorials from lxus guy) but again I'm not sure what the think of. Tell me this when you are doing 40-50 mph on a straight road what is your idle shows? mine is around 1000 even less.

If you think this is a sensor issue (but like you said light should come on) how to fix or change the thing do you know?

Thanks again

[Shadow]

91LS: 2000RPM @ 60mph

First try to see if the problem is in the sender or receiver (gauge). This won't be easy if you don't have proper equipment and technical info.

[Salacak]

I don't have proper equipment but what should I look for or how to fix it if something I can do?

I don't want a end up dealers hands, I rather stay and drive the way it is but if anything simple or I can handle why not I'll give it a try.

[Shadow]

RPM gauge gets its signal from the igniter #1. You can attach an external rpm gauge to the igniter #1 and compare the RPM readings. If they both read the same then it's the igniter which I highly doubt since the ignition coil get their signals from the igniters also. Bad igniter signal would translate to bad coil signals, thus, bad spark on the plugs. Alternatively, you can also compute the RPM by attaching a scope to igniter #1 and observe the duty cycle and compute the RPM and compare.

I highly suspect the problem lies in your gauge, more specifically, the capacitors. Change those CAPS will do wonders to your instrument panels. The good part is CAPS are cheap and relatively easy to replace if you can solder.

[Salacak]

Thanks for the reply and good information, I believe motor vehicles equipment was correct because when guys told me to push on the gas pedal until 2500 RPM I did it and my RPM was showing 1200 when his was 2500 and I believe his was right (Testing 100+ cars a day). Some how my RPM show low numbers because when I'm doing 50 mph still stays around 1000 RPM proves that I think.

But still I don't know where to start and what to look for.