High/revving idle on cold motor..

LukeZ34 · November 23, 2004, 10:38:03 PM

Jess's TGP has developed an odd problem.
Upon starting the motor cold, the idle will slowly creep up to 1500-2000 RPM (sometime it spikes directly up to 2K). It's not a steady idle, it fluctuates on NO pattern up and down a couple 100 RPM while it's idling high. BUT, once the car is put in to gear, it idles fine. Whether it be while driving, or coming to a stop and putting it back in to Park, it idles fine.
It's had this problem off and on for a couple of weeks. The first time we noticed it, the problem wasn't just a high idle in Park, it also wanted to idle higher in any drive gear. I unplugged the battery for about 20 minutes, and then reconnected it, and it started up perfectly fine and the problem didn't come back for another week.
She had to drive an hour and a half on interstate this morning to Salina. When she started it in the morning, it idled high for a while, and then eventually settled back down to a normal idle (around 1K). When she got to Salina she stopped someplace, and then started the car shortly after that to leave, and it idled fine.
It's a real come and go problem, and it's got us baffled as to what the problem is. The IAC valve is only about 6 months old, and the TB passages are clean. The upper intake gaskets are new, as is the TB gasket. The way it fluctuates at idle, it seems like the ECM is having problems. She has a TG160, and we haven't tried putting the stock chip back in to see if that stops the problem.
Anyone got any advice? It's much appreciated.

god910 · November 24, 2004, 07:37:24 AM

I'd take the IAC out and clean the pintle and the seating surface. Then I would unhook the battery, reconnect, and start her up. Scan it and check the IAC counts. If everything is working okay, you'll have a good baseline. Then when it starts to act back up, pull out the laptop and check it out again. See what's going on. If it doesn't come back. It was probably just some carbon on the pintle. Good luck.

SpeedDemon · November 24, 2004, 01:01:24 PM

Did you reset the IAC valve? I just put one on about two months ago. you have to turn the key to the on position for 5 seconds (but don't start the car) then turn it off for 10 seconds (that resets the IAC). After you have reset the IAC you have to take the car above 40 mph to get it to seat correctly (if not the computer will not know when to close off the vacuum port) .

z284pwr · December 07, 2004, 01:55:40 AM

Not to steal the thread or anything but I've had the similar with my TGP ever since we put the new engine in the car, even with about 3 different IAC motors it still idles high in park while its cold, and does it EVERYTIME.... It will idle high until I put the car in drive, and then will finally idle normal when I put it back in park. I have tried the idle relearn with the TopGun Chip to no help? Any ideas?

R Dubya · December 07, 2004, 06:39:15 AM

I have had the same problem with mine since I put the engine in in late August. I haven't driven it in over a month, but that will be priority number 1 when it comes out of the garage. That's hard on the tranny. I think it's a vac leak.

Jeff M · December 07, 2004, 11:57:34 AM

Luke, what numbers/words are written on the TopGun 160 EPROM :?: :?:

God910 had this same problem and I told him the chip (stock or mine) has a table to compensate for a Low Battery Voltage condition, that bumps up the IAC Motor/Idle Speed when voltage drops too low. I suggest to everyone with this problem to also check their Charging Volts :!:

Jeff M

dbtk2 · December 07, 2004, 06:03:45 PM

Mine has done this since I did my topend swap. All the sensors were either new or cleaned. It doesn't make any difference if I unplug the sensors either. But I have a brand new battery and brand new alternator and it charges just fine and it won't idle down until I drive it. I disconnected the battery and let the chip learn, and this worked for about a week and a half and then it started up again. I can't find the problem.

Shawn

Jeff M · December 07, 2004, 08:59:00 PM

Quote from: dbtk2Mine has done this since I did my topend swap. All the sensors were either new or cleaned. It doesn't make any difference if I unplug the sensors either. But I have a brand new battery and brand new alternator and it charges just fine and it won't idle down until I drive it. I disconnected the battery and let the chip learn, and this worked for about a week and a half and then it started up again. I can't find the problem.

Shawn

3 things come to mind right off, a grounding problem, the IAC is closed with the throttle plates too far open, or the IAC tables do not like your new setup-intake/cams....or since you have a different intake AND cam, you breath different too.....so, more air (with more fuel) needs more timing to burn all this......, or since on the compression stroke you compress this "more air" higher and you take the timing down instead, guess you will have to decide 8)

Jeff M

SpeedDemon · December 07, 2004, 09:03:55 PM

OK, I work as a lot tech for the chevrolet dealership by my house and I get to drive and move the cars around in the lot. Even the 2004 idle high when you first start then. My guess is it kind of acts like a choke when you start the car (just my thought). So it doesn't seem to be a problem. Also if your tach is off then its going to look like its idling higher than it really is. But for the most part its normal (IMO).

z284pwr · December 07, 2004, 11:48:33 PM

Quote from: SpeedDemonOK, I work as a lot tech for the chevrolet dealership by my house and I get to drive and move the cars around in the lot. Even the 2004 idle high when you first start then. My guess is it kind of acts like a choke when you start the car (just my thought). So it doesn't seem to be a problem. Also if your tach is off then its going to look like its idling higher than it really is. But for the most part its normal (IMO).

Mine will actually idle high ~2500 or so UNTIL i put the car in drive.....

TurboGTU · December 08, 2004, 12:37:36 AM

My GTU and Nitrodaves old TGP idle fine at start up. Well the TGP idles like at 1500 and comes back down and stays there after a few seconds. The TGP did have a lightly dischaged batt..but it stayed fine in idle without putting into gear to fix the high idle. Mind you with bad coils, bad turbo :? A ALDL scan would be nice.

LukeZ34 · December 08, 2004, 02:29:43 PM

Whoa! This took off! :shock:

Jeff, it's funny you mention the charging volts. I've noticed the lights have been a bit dim lately.
Her car has been sluggish lately too, and there's a whining coming from what sounds like under the hood. I can't tell if it's alternator whine because it only does it while driving AND accelerating. If your not driving (aka sitting idle), revving the motor will not reproduce the whine.
I'll check her charging volts, and post the EPROM markings on here. I need to check my charging volts anyway since my headlights are getting dim on the 5 speed.

Jeff M · December 08, 2004, 06:09:35 PM

Lets hope its charging volts, cables etc, easier then the other guys with their problems 8) You can also check the ground and power cables by measuring the voltage drop DC from one end and the other of each main cable. Fire up the engine, throw on a load such as headlights, have the woman idle the engine at 1,500 rpms then measure for DC Volts from each end of the ground cable (battery and engine) should be .1 volts DC or less, preferable less than .1 :!: Same running condition for power, grab from the alternator feed/at alternator and at battery positive, you can have up to .5 VDC, preferable less. If you failed the ground test, time to yank all of them and test the strength of the connection of the cable to connector/spade, clean all contact areas if cable to connector are good and tighten back down/re-check voltage drop (I like to grease them to stop moisture and corrosion from happening later as it does!!). Power cable, same checking and cleaning though I need to check a known good setup I have to see if our cable is a little undersized which it looks like to me and with the length of the run!! To check your alternator other than its charging volts, which should be 12.8 to 14.5 (idle with no load, load with rpms up) set your volt meter to AC and check the voltage, all alternators put out some AC current/volts but if you get .5 VAC or more, diodes are failing, time for a rebuild! IceBurg makes a 140 amp upgrade kit (not a complete alternator, just to upgrade and rebuild yours), Delta Y double wire wound armature, and cast into the rear case, heat fins for the rectifiers mounted there on the flip side, and a larger 10mm high-temp grease rear bearing. Powermaster also but cost big bucks but seen theirs has a 4 wire armature and the same 140 amp rating but at idle it puts out 90 amps which is more than most upgrades do and this rating goes up faster towards the 140 amp max rating. All right, I need to shut up and get some other work done.

Jeff M

dbtk2 · December 08, 2004, 09:00:38 PM

Quote from: Jeff M3 things come to mind right off, a grounding problem, the IAC is closed with the throttle plates too far open, or the IAC tables do not like your new setup-intake/cams....or since you have a different intake AND cam, you breath different too.....so, more air (with more fuel) needs more timing to burn all this......, or since on the compression stroke you compress this "more air" higher and you take the timing down instead, guess you will have to decide 8)

Jeff M

I thought maybe it was because of the topend too, but if I relearn the idle then its fine for a week or two. And it ONLY does it until you put the car in gear, once you put it in gear its fine. When you put it back in park or neutral the revs are down where they are supposed to be. It will start out around 2k-2500rpm, when you put it in drive the revs drop to like 1000 or less and its fine after that. I know I need to get the chip tuned for the stuff, but I don't think thats the whole problem. I don't remember for sure, but I think the car might have been acting up before the topend swap as well, but I know its been doing it AT LEAST since the swap.

Shawn

z284pwr · December 08, 2004, 10:25:25 PM

Quote from: dbtk2
Quote from: Jeff M3 things come to mind right off, a grounding problem, the IAC is closed with the throttle plates too far open, or the IAC tables do not like your new setup-intake/cams....or since you have a different intake AND cam, you breath different too.....so, more air (with more fuel) needs more timing to burn all this......, or since on the compression stroke you compress this "more air" higher and you take the timing down instead, guess you will have to decide 8)

Jeff M

I thought maybe it was because of the topend too, but if I relearn the idle then its fine for a week or two. And it ONLY does it until you put the car in gear, once you put it in gear its fine. When you put it back in park or neutral the revs are down where they are supposed to be. It will start out around 2k-2500rpm, when you put it in drive the revs drop to like 1000 or less and its fine after that. I know I need to get the chip tuned for the stuff, but I don't think thats the whole problem. I don't remember for sure, but I think the car might have been acting up before the topend swap as well, but I know its been doing it AT LEAST since the swap.

Shawn

This sounds a lot more like my problem, i never noticed it as much before the engine swap, but ever since the new engine has been it, it as definitely had the problem?