1G high idle surge only after warmup

[patriot]

upon startup, the idle is perfect. bout 8 degrees advanced, 750-775 rpm, with no surge whatsoever. at approximately warming up to 180 to 185 degrees, the engine starts to surge from 2000-2500 rpm, advancing to ~30 degrees timing. i can unplug the maf, which throws a code, but the idle regulates back down to about 700 rpm with no surge. ive done a boost leak test and it holds all pressure up to about 25 psi, then you can hear it leaking in the throttle body. i got an extra 2g maf and had the exact same symptoms. i got a brand new ISC motor... no difference. it acts like a major boost leak, but with the test i dont see how this can be a factor. one thing i did notice on my logger is that the EGR temp was negative 18.5 degrees from startup even. the EGR is blocked off.

with this happening at almost exactly 185 degrees, i would think my FIAV may be defective. would this EGR reading also be a problem? im open to ideas here as to which direction to go from here guys, thanks.

 

[talontd92tsi]

Check your BISS, Mine had backed all the way out, luckily it didnt fall out, it did the same thing you are describing. Just remember adjust your idle correctly by grounding the plug behind the battery, and the one next to the fusebox under the dash, let it warm up completely, then screw your BISS down till your idle is where you want it, unground the connecters, and your done.

hope this helps

 

[patriot]

biss has no effect whatsoever on adjusting the idle, it does have a new rubber o- ring. also did a boost leak test after warm and no leaks up to about 25 psi. TPS reads 11.3% throughout.

 

[patriot]

ok, finally got a CEL. it reads 12 on the datalogger, so i think on a 90 model that means an injector problem. not sure what all a '12' entails, but im lookin into it. suggestions always welcome!

 

[patriot]

actually 12 is for the maf... which i didnt have pluggen in all they way . anyhow, installed new isc, different maf, plugs(maintenance while i was at it), triple checked to make sure the 1g to 2g maf wiring was correct, checked all maf wires for continuity, replaced the throttle body with a rebuilt one that has all new seals, lined up all timing marks at TDC, tested and retested for boost/vac leaks........ and still have the idle problem.

anyone?????????

 

[patriot]

compression is 125 on all 4 cyls

 

[gixx1000]

O2 sensor maybe?

 

[Gromit]

upon startup, the idle is perfect. bout 8 degrees advanced, 750-775 rpm, with no surge whatsoever. at approximately warming up to 180 to 185 degrees, the engine starts to surge from 2000-2500 rpm, advancing to ~30 degrees timing. i can unplug the maf, which throws a code, but the idle regulates back down to about 700 rpm with no surge. ive done a boost leak test and it holds all pressure up to about 25 psi, then you can hear it leaking in the throttle body. i got an extra 2g maf and had the exact same symptoms. i got a brand new ISC motor... no difference. it acts like a major boost leak, but with the test i dont see how this can be a factor. one thing i did notice on my logger is that the EGR temp was negative 18.5 degrees from startup even. the EGR is blocked off.

with this happening at almost exactly 185 degrees, i would think my FIAV may be defective. would this EGR reading also be a problem? im open to ideas here as to which direction to go from here guys, thanks.

Have you read this big write-up?

http://www.dsm.org/how-tos/tttt/tttt3.html

Lots of info there on different causes of idle surge. And when you say that you're at 8* advanced during warm-up, you're talking ignition timing there. Is that the number you're seeing on a logger? If so, check your timing via a timing light & verify that it is at 5* BTDC with the plug grounded (ungrounded you will see approx. 8* with the light). Also, your compression is near the lower service limit - did you perform the compression test on a fully warmed up motor? Did you also do a wet test?

 

[patriot]

thanks for the replies guys. i did the compression test after warmup. im not sure why the readings are so low, as there is about 2k miles on the rebuild, bored .020 over and new pistons. it is low, but still in spec though, and exactly the same on all 4. terry's troubleshooting was one of the first i have dealt with, and have referred back to it a couple times, rechecking to make sure i tested everything correctly. the timing is at 5 btdc with the pins grounded. vac is at 18 hg, and when the surging starts, it ranges between 14 & 19, about once per second to give you an idea how fast. i have not done a wet test. the 02 sensor has been replaced already, and has the same readings as the old one according to the logger.

 

[patriot]

ok.. last day of vacation wasted apparently, . i have eliminated two boost leaks, and one vac leak. the boost was at the turbo to intercooler gasket and the bov, and the vac was at the aeromotive regulator adj screw..... however all three were pinhole and have not made a difference to the surge. i also switched back to a stock thermostat, also no difference. the one thing i thought might make a little difference, at first disconnecting it and then rewiring it properly, was the afc. again i was disappointed as either configuration produced the same surge. i now know i have absolutely no vac leaks, and no boost leaks up to near 28 psi.. didnt want to go any higher than that for fear of blowing a gasket somewhere.... and my air pressure hose kept blowing off because it was holding pressure so well, hehe.

at this point im thinking my ecu might be having some issues, im not sure what else could cause this.

 

[dvbrien]

How long have you had the car... How long have you had this issue... Reason I ask is because I had a similar problem. I noticed I had a 90 ECU in a 91 Car when I swapped the ECU with the 91 Eprom it stopped. I am certain the other ECU was good because I installed it in a 90 with a bad ECU and it fired up and drove like a bat outta hell! NeWay check you ECU year because if you have a 90 car and 91 ECU you have a couple of wires you'll need to switch around to make it right... and check your O2 wiring if factory harness plug has been cut. ISC is always a suspect here too but, this is as obvious as boost leaks I know you've checked it.
Caio Bro.

 

[patriot]

ive had this tsi for about 6 or 7 years i guess, and this has been a growing problem over several months. probably about a year ago, id start stalling at stop lights, or if i let of the gas quickly. one would immediately think isc... so after about 3 isc's, the original ecu finally burned up on me. i have since learned that if you stick a good isc in a car with a bad ecu.... pretty soon the new isc will burn up. so i got a rebuilt ecu. i have since learned that if you have a good ecu in a car with a bad isc, then pretty soon you could have a bad ecu also.....

so, now i have a new ecu, a new isc, a rebuilt throttlebody, every gasket checked, blah blah blah.

i am currently converting the 90 to a 93 eprom. guess ill just have to see from there

 

[dvbrien]

alright... just wanted to throw this out there too not common but a possibility, Check you exhaust ground strap. Reason being, if you O2 sensor is getting ground from this stap but the strap is broken... consequently the O2 sensor would not be getting power, possibly causing the irratic idle.
Daniel

 

[patriot]

i dont even think i have a ground strap anywhere on the exhaust... i am getting a signal on the logger from the sensor, though. ill look into that, thanks.

 

[dvbrien]

You have to read this... All about the Idle problems... http://www.dsm.org/how-tos/tttt/tttt3.html
Daniel

 

[patriot]

that is the first guide that i printed to determine my problem. this is where im stuck accroding to the guide:

#4. Ok, no vacuum leaks, but it's still surging
You still have too much air getting past the TB, but you have narrowed the number of possibilities down to 4.
There are only 5 normal ways for air to get past the TB: The throttle plate, the base idle speed set screw (BISSS), the ISC, the fast idle air valve (FIAV), and the EGR valve. You already cleaned the throttle plate and made sure it closes properly, that eliminates 1.
With the engine running and hot (temp>=180), pop the rubber plug off the front of the TB to expose the base idle speed set screw (BISSS). Disconnect the idle switch and the ISC connector so the engine runs at a steady speed and the ECU can't fiddle with the ISC without your knowledge. Count the turns of your screwdriver as you screw the BISSS closed (clockwise). The RPMs should drop. Have a friend watch the tachometer to tell you when it reaches 750. If you run out of screw before the engine drops to 750, back the screw out to where you found it. Replace the rubber plug.

when i disconnect the isc and idle switch, the idle only barely drops to about 1500 rpm before bottoming out with the biss screw. with absolutely no leaks, im not sure where to go from here. the only thing im not sure how to test is the fiav. but i now have 4 90 throttle bodies, all with working sensors. i tried the other three just thinking ok something may be wrong with one or two of them that im just not seeing... all sensors, besides the fiav test good on all throttle bodies, i have the same surge with all throttle bodies. i dont think my problem has to do with the throttle body.

after rereading it again, i have come to one conclusion though, i might have too much air coming in from an intake leak somewhere... as this cant be tested with my boost leak tester b/c of course the intake is removed. im going to try and remove the maf and rig a way to connect the boost tester to the end of the intake itself, actually ill probably just spray some carb cleaner on the intake couplers first, then try the boost test if that proves nothing.

hopefully i can get this taken care of soon, as the new chip and ecu conversion to a 93 eprom will be here next week, along with a mafT.

 

[dvbrien]

Is your ECU mounted in the original position? http://www.dsmtuners.com/forums/showthread.php?t=81176&highlight=ecu+ground

 

[patriot]

the ecu is mounted in the original position. i have since gotten the chip for the eprom that i had, and a coil pack adapter plug from keydivers. hooked it all up, started, warmed up...

the good news is, the surge is gone and my idle dropped to a steady rpm.

the bad news is, the rpm is at 1000 with the timing adjusted all the way retarded(still at 8 degrees) and the biss screw all the way in.

i wish that was totally the cure, but i must say im happy with progress.

 

[patriot]

well, surge returned again, but not quite as bad. 1200-~1700... so, i hooked up the boost leak tester one more time, and cranked it slowly up to about 30 psi... due to not finding anything else wrong with anything electronically, and found a minute leak from the corner of the intake manifold gasket ... not sure if this is my problem, but got a heat barrier gasket anyways as a replacement for the paper one from SBR. just got it in the mail and will be installing it tomorrow hopefully.

 

[patriot]

installed new phenolic intake mani gasket, b/c that was the only leak.... cranked it up, same idle fluctuation. tested vac lines again, everything holds at ~20 psi with no leaks whatsoever.

i cannot think of anything i have not now tested, used the idle guide referenced earlier, and still have the problem. the only thing i have not been able to test is the reed switch, the speed sensor. could this even possibly cause my symptoms of a fluctuating idle???

 

[90 GSX]

Try adjusting the idle properly. Ground the timing connector and the two pins on the ECU diag. harness and set the idle to 750 on the logger if you have one. Plugging in a logger automatically puts the ECU in diagnostic mode so then you just have to ground the timing connector. Make sure the car is fully warmed up (and driven for a while).

Also, if the IPS, ISC, ECU, are all good and you have no boost leaks, it may be a bad FIAV in the throttle body. That would require replacement of the entire TB because a 90 FIAV can't be blocked off.

Also, verify your base timing.

 

[patriot]

ive done all that man, and thanks for replying. the problem is, after the motor is warmed up, with the logger connected, and the timing connector grounded in the engine bay, the cas turned all the way retarded, and the biss screw all the way in, im still advanced about 10 degrees. wtf??? i have four 90 throttle bodies with 4 sets of tested good sensors... the idle is the exact same with each TB. im currently wiring the maf back to the stock plug.

and update: now as soon as i turn the key before i crank it, my radiator fan comes on. i am guessing this means the ecu thinks the coolant is too hot all the time??? ive replaced the engine temp sensor and the ac idle switch in the thermostat housing, the only one i havent replaced yet is the one on the bottom of the radiator, which will be done in an hour or so.

 

[patriot]

well, i do think every sensor on the car that could affect the idle now is new... and yet i still have this problem. the only thing i can possibly think of is that my intake manifold has a hairline crack in it or something. guess ill pull it... again. this sux, very nice 90, and cant drive it, halfway reliably anyways.

 

[patriot]

ok now i have the maf cel again. ive since switched to a gm maf. i had an old maf which gave good signal for about 20 minutes, then the translator led went out which meant it was no longer receiving a signal from the maf... so i just bought another gm maf thinking the one i had was gone... installed it, and after about 20 minutes of running.... no signal from the maf again! . this is of course throwing a cel on top of my other damn problem with the idle surge. so i guess im going to completely trace the wiring from the maf to the ecu before i put in another maf, fix the cel first and then move to the idle problem which doesnt throw a cel . this damn talon is killing me, im seriously debating parting it out just b/c of this intermittent, phantom ass bullshit.