'04 low idle issue

dcorwin822 · Post by **dcorwin822** » Fri May 11, 2012 6:43 am

2004 atx base neon.

It has a low idle issue that I can't seem to resolve. It happens mostly when the car is up to temp. The idle drops to 500-600 rpm and the entire car vibrates. Holding the brake and tapping the gas puts the idle back to where is supposed to be for a smooth idle. I dont have to really tap the gas much, any thing to bring the RPMs above 1k works.

I don't feel that drilling a hole is the plate is a proper "fix" to something that was working fine w/o the hole.

I've replaced plugs, wires, cam sensor, and have had the cooling system re-done as well (new stat and relive cap), the o2 sensor was replaced about a year ago but it's switching fast enough when i'm looking at it with my scan tool. I've cleaned the throttle body, the idle control valve and have done a seafoam treatment and the MCCC thing as well.

I've redone the transmission fluid four times now sense about 2 years ago when the radiator mixed the fluids.

Got any ideas?

Kelevra · Post by **Kelevra** » Fri May 11, 2012 8:32 am

My neon would, and still sometimes does drop to around 600-700 RPMs at idle but never below that. I don't notice it as much now with a 'new' IAC but with my old one it would nearly constantly be at 600-700 at a stop/idle. if you're really that worried, pick up an IAC off a friend or from a JY but don't drill into the throttle plate....

Marmelade Boy · Post by **Marmelade Boy** » Thu May 17, 2012 1:41 pm

Yeah, I wouldnt drill a hole. Occasionally my car did this, until I re routed my brake booster line and replaced the 90 degree elbows with just a straight hose. and it hasnt been below 600-700 since.

Johny · Post by **Johny** » Thu May 17, 2012 1:45 pm

Mine does that too, sits at 6-700, I dont really think much of it. Toss it in neutral when it happens, it should go back up

Gnuserup · Post by **Gnuserup** » Thu May 17, 2012 3:06 pm

Seems to be really normal on 4-speed. My SXT does this as well. Usually something around 600 +-50. But I notice if I switch AC on or steer the idle goes up a bit. If Ishift in neutral the idle goes onto 800 or something.
My manual LE always runs at about 900, I believe same on a 3-speed, but could get a look tomorrow if really.

gcretro · Post by **gcretro** » Mon Jun 18, 2012 8:16 pm

Marmelade Boy wrote:Yeah, I wouldnt drill a hole. Occasionally my car did this, until I re routed my brake booster line and replaced the 90 degree elbows with just a straight hose. and it hasnt been below 600-700 since.

can you explain this re-route? and the elbow. I have an 04 Neon SE and have same issue when parked in drive at a stop light.

Post by **occasional demons** » Mon Jun 18, 2012 8:57 pm

He probably just replaced the molded brake booster line with a regular length of vacuum hose.

It probably had nothing to do with the idle problem. Unless there were leaks the IAC was over correcting for.

There isn't any actual air flow through that line. Just what the brake booster needs.

gcretro · Post by **gcretro** » Tue Jun 19, 2012 8:07 pm

Can aging/bad spark plug wires a strong reason for the idle undershoot? (any way to check the plug wires say for resistance with a multimeter? and if there are limits to the values?)

Post by **occasional demons** » Tue Jun 19, 2012 10:51 pm

Yep, you can ohm them out.

#1, #4 = 3500 to 4900 ohms

#2, #3 = 2950 to 4100 ohms

Don't know that they would be a direct cause of idle undershoot tho.

dvon17 · Post by **dvon17** » Wed Jun 20, 2012 12:34 am

my car always idle's between 500-600rpm. I didn't know it was that bad of a thing lol.

#noob

Post by **occasional demons** » Wed Jun 20, 2012 7:08 am

Only if it bothers you.

With an ATX, it can be annoying, especially in drive, as it can shake and rattle pretty intensely. It more or less depends on where the IAC valve is at the lower RPM.

Mine can idle smooth as glass at 500 rpm, or it can shake like a dog shitting razor blades. Just depends on what mood it is in. Usually worse with A/C on. But it can pull up a hill at 500 rpm and not shake one bit.

I have also noticed when it does idle low, in gear, it is almost dead silent.

dvon17 · Post by **dvon17** » Wed Jun 20, 2012 10:45 am

Yea. Mine is dead silent too. Sometimes I look down to make sure it didn't shut off lol.

So, I guess I like it. Also, with my a/c on...the only time the car has issues is when its in park and idling for a minute... it'll shake a little...never in gear.

It also bogs as soon as it shifts t 2nd gear with the a/c on. So I'm always sure to let it take its time. Don't wanna hurt my baby lol.

Nevertheless... I like it idling low. Especially if it isn't causing any problems.

Donkeypuncher · Post by **Donkeypuncher** » Wed Jun 20, 2012 1:06 pm

Yeah 2nd gear can be interesting with the a/c on, the rpms drop like a rock so you have to finesse it a little to get a smooth shift.

I understand the hesitance to drill a hole in the throttle plate, but it did help my idle. It was suggested by ed peters, otherwise I wouldn't have tried it.