Idle surge ONLY after warmed up. Causes??

[tsi1991awd]

This is the complete opposite from idle surge issues I have had in the past. Before, I would get surge when it was cold but once it warmed up it would go away. This time, it idles just fine until the temp gauge is almost to the middle of the gauge.

Once it warms up, the idle bounces between 1500 and 1800. If I disconnect the IPS, the idle will stay consistant at around 2000. While it is surging, I disconnected the ISC and nothing changed whatsoever.

I did a BLT and found two leaks...one right before the MAF (3" GM MAF) and one right after the MAF. I fixed these leaks and thought it would fix the problem....nope, problem still exists.

I have the EGR blocked off with a plate. Throttlebody is a 1990 and the FIAV is blocked off. ISC is a blacktop instead of the 90 one with pigtail. O2 sensor is a brand new NTK unit. Throttlebody shaft seals were already replaced, new BISS screw, new throttlebody gaskets.

There are no boost leaks anywhere, no leaks at the throttlebody or intake manifold or injectors. Could this issue be caused by a bad CTS?? Or where should I start?

 

[92AWDHX40]

Terry's Talon Troubleshooting Tips #3 - Fast Idle (aka. Idle Surge) Check this out, i used google and did a search, lots of information on dsm idle.

 

[Texas gst]

Possible vacuum leak.

 

[tsi1991awd]

Terry's Talon Troubleshooting Tips #3 - Fast Idle (aka. Idle Surge) Check this out, i used google and did a search, lots of information on dsm idle.

I've already read over that. So basically the only thing from that is that it would be my ISC. The ISC tested fine but I guess maybe it is like his problem and only does it when warm

Possible vacuum leak.

All emissions equipment is removed, all vac lines are blocked off, no boost leaks as mentioned above.

 

[92AWDHX40]

Throttle body, issues, mine wont idle either but i have all winter to figure it out, getting dsmlink also, real soon, to help out. Check the fiav, all i can say is to keep trying things.

 

[tsi1991awd]

Throttle body, issues, mine wont idle either but i have all winter to figure it out, getting dsmlink also, real soon, to help out. Check the fiav, all i can say is to keep trying things.

As I mentioned above, FIAV is already blocked off. It's a frustrating issue.

 

[sprmotohooligan]

Just throwing it out there... Idk if the 1G's have cruise control. But I'd get crazy high idle while driving at low speeds and traffic sometimes b/c of the cruise/throttle cable sticking a little bit and not returning all the way.

 

[tsi1991awd]

Just throwing it out there... Idk if the 1G's have cruise control. But I'd get crazy high idle while driving at low speeds and traffic sometimes b/c of the cruise/throttle cable sticking a little bit and not returning all the way.

Deleted the cruise and went with a brand new non-cruise cable. It doesn't stick at all and it glides smooth as butter.

 

[gusu]

If your ISC is stuck that is one cause. Another common issue is people have their ISC stuck so long it ends up frying the ECU so the ECU will cause the idle surge. Putting on a new ISC on a bad ECU will kill the ISC from what I have been told. The wrest I know to be true the last part I'm not to sure about.

I'm currently in the same boat. I have done EVERYTHING there is to do pretty much. I noticed my fuel cuts out at the top of the surge. Is your AF doing anything weird?

 

[tsi1991awd]

What gets me is it will idle just fine until it reaches almost to the middle of the temp gauge (stock gauge) and then the idle will slowly raise up to 1800 then surge from 1500 - 1800....very weird.

 

[feardafish]

I am having the same exact problem, have been driving all winter, a few days here it was -19 degrees without windchill and she ran GREAT. few days after that bitter cold it warmed up to about 34-36 degrees outside. Started her up, and 5 minutes of warming up started to surge. It has been over 35 degrees for the past few days here, and its still surging. I read the talon guide for idle surge and replaced my ISC, no change at all. I also had my ECU replaced due to recall about 6 months ago. Of course theres tons of info on that guide and it seems like 101 things that can cause this problem, once i get more time ill be trying the FIAV and all. If it were a vac leak i would imagine the surge should start immediatly instead of only when its been idling for bout 5 minutes.

It is very strange though that it has been running fine for a year and a half through 2 winters, and as soon as it gets alittle warmer outside it starts happening.

 

[Wardog]

Was this ever resolved? its been a couple of years now, but I'm having the same problem.
It runs/idles a bit high when its cold but runs fine considering 272 cams and all that, but when the engine gets some temperature in it it starts to surge, from around 15-1,600 - 2000 area. EGR has a block off plate, that has been checked. When i disconnect TPS it goes to a steady 2k RPM, stabilises a little, then starts surging again. Its a really annoying problem, so did any of you sort this out that can possibly give me a pointer to what more i can check.

Btw i have read terrys list, and a good post in here, I'm just asking since I'm working on the list, just wondering what was the solution to you guys.

 

[spyderdrifter]

Conduct a leak down test, and a compression test. That'll show you where you're surging from. Leak Down Test VFAQ
How to do a Compression Test

 

[The Sun]

Hello, my Del Sol is doing the same thing. Ive even replaced the whole motor/intake manifold, thinking all the little problems like the high/erratic idle after warm-up would stop, but the problem still persists. I've run out of ideas. I've tried to fix the timing and it did return to normal rpms, but only for a day. Anyone who can help is appreciate it.

 

[spyderdrifter]

Although a Del Sol isn't a DSM, you should still do a leak down test. That will tell you where you're leaking air, if at all. Then check your sensors after fixing air leaks.

 

[Happys_TSI]

This is the complete opposite from idle surge issues I have had in the past. Before, I would get surge when it was cold but once it warmed up it would go away. This time, it idles just fine until the temp gauge is almost to the middle of the gauge.

Once it warms up, the idle bounces between 1500 and 1800. If I disconnect the IPS, the idle will stay consistant at around 2000. While it is surging, I disconnected the ISC and nothing changed whatsoever.

I did a BLT and found two leaks...one right before the MAF (3" GM MAF) and one right after the MAF. I fixed these leaks and thought it would fix the problem....nope, problem still exists.

I have the EGR blocked off with a plate. Throttlebody is a 1990 and the FIAV is blocked off. ISC is a blacktop instead of the 90 one with pigtail. O2 sensor is a brand new NTK unit. Throttlebody shaft seals were already replaced, new BISS screw, new throttlebody gaskets.

There are no boost leaks anywhere, no leaks at the throttlebody or intake manifold or injectors. Could this issue be caused by a bad CTS?? Or where should I start?

This is the complete opposite from idle surge issues I have had in the past. Before, I would get surge when it was cold but once it warmed up it would go away. This time, it idles just fine until the temp gauge is almost to the middle of the gauge.

Once it warms up, the idle bounces between 1500 and 1800. If I disconnect the IPS, the idle will stay consistant at around 2000. While it is surging, I disconnected the ISC and nothing changed whatsoever.

I did a BLT and found two leaks...one right before the MAF (3" GM MAF) and one right after the MAF. I fixed these leaks and thought it would fix the problem....nope, problem still exists.

I have the EGR blocked off with a plate. Throttlebody is a 1990 and the FIAV is blocked off. ISC is a blacktop instead of the 90 one with pigtail. O2 sensor is a brand new NTK unit. Throttlebody shaft seals were already replaced, new BISS screw, new throttlebody gaskets.

There are no boost leaks anywhere, no leaks at the throttlebody or intake manifold or injectors. Could this issue be caused by a bad CTS?? Or where should I start?

I'm having the exact same problem but it will only surge if you let it idle until temp gauge is almost most half way to the middle. If you drive it while it's surging about 10 mins into driving it will go away and idle perfect. But if you cold start it and rev it a little bit the surging will start Immediately. But if you start it and drive it right after starting before the surge starts, it will idle perfectly fine at 1000rpms. I adjusted the biss didn't seem to do anything but the biss is bottomed out. When surging it bounces from 1600 to 1200 and it does it in a rhythm. When rpms drop to 1200 it sounds like the car wants to die then jumps it back up to 1600. Any ideas on what it could be?

 

[93AWDDSM]

Please, please do a boost leak test. I know it’s such a broken record but it can mess with idle (high idle, surging) quite a bit if it’s leaking metered air before using it.

 

[PlanZero]

When the idle is rhythmic it's usually IAC/ISC related. Unplug it to see if there's a difference when this is going on. If you still have a tan IAC replace it. They're know to be problematic and can fry your ecu. I get mine from this guy. Can't beat a lifetime warranty on used parts.
https://m.ebay.com/itm/Mitsubishi-3...952746&hash=item25e290ba05:g:~ecAAOSwlQlZ5S3A

 

[chrysler kid]

Ok so in my chasing this exact problem I have found the solution

Issue: after 30 seconds idling the rpms jump up to 1500 and the biss screw is already turned all the way in

I replaced my throttle body, cleaned it, re sealed it, tried 3 different iac valves, adjusted fiav, calibrated tps, you name it

Im not sure why I needed to re adjust my throttle body stop screw, the head has been off the car 3 times this year, so im sure that had something to do with it. Maybe my head getting fixed increased the engine vacuum and I needed to lower the amount of air going in by increasing the throttle restriction.

I fixed it

The biss and iac are run together. The biss screw does not set your base idle

How I fixed my problem

With the car idling loosen the throttle bracket on the intake manifold. Get an 8mm deep socket and 1/4 ratchet. Loosen the throttle stop screw bolt, DO NOT ADJUST THE SCREW. With the bolt loosened you can spin the nut and the screw out together slightly then depress the throttle body to close more.

At this point your idle will drop. Do not set the throttle stop screw yet. If you set the screw now you will need to re calibrate the tps. Also you will notice your idle is now lower but also much weaker, trying to merely set the new throttle stop will not result in a stable idle, it will either be too high or too low.

You should now notice the biss screw is now able to be turned out slowly to increase your idle. Slowly turn it out to set a good start to your new idle

As a side effect the biss screw will now have a large effect on the iac. The biss screw determines how much air the iac lets into the motor. As you turn out the biss screw you will notice now the iac is causing the rpms to bounce up and down every 10 seconds or so

With a good base top idle in the fluctuating range turn back in very slowly the 8mm bolt for the throttle stop bolt. As it goes back in you will need to gradually turn back in the biss screw to offset the throttle body opening back up again.

The more you turn back in the 8mm throttle stopper screw the more you can fine tune the iac and the amount of air it lets into the engine when the iac is used.

Eventually you will get a balance, the car will have a strong setting and idle will not fluctuate. After balancing the iac with the bss against the throttle stop you will need to use the .0177 feeler to set your tps to find zero

If youre confused, good. Dont go messing around with this unless you understand the terms I described

You cant just turn down the throttle stop screw, it Wont balance itself. The throttle body is not exact enough to set idle, which is why you need the idle air control valve. It sets a strong idle

 

[PlanZero]

^although this fix may be necessary I found that adjusting the stop screw only helped recalibrate the BISS, which only helped on a consistant high idle situation. This is usually a last resort fix unless you've done something significant such as removing the head (for me it was the built motor)

The OP has a rhythmic, bouncing idle indicative of a faulty IAC or even TPS. When the cars warmed up unplug the TPS or IAC and you'll hear the difference. OP may also have to recalibrate his TPS after replacing the IAC. I've found that even the black IACs can act very squirrley and need replacement, whereas usually the TPS just needs adjustment instead of replacement.

 

[chrysler kid]

^although this fix may be necessary I found that adjusting the stop screw only helped recalibrate the BISS, which only helped on a consistant high idle situation. This is usually a last resort fix unless you've done something significant such as removing the head (for me it was the built motor)

The OP has a rhythmic, bouncing idle indicative of a faulty IAC or even TPS. When the cars warmed up unplug the TPS or IAC and you'll hear the difference. OP may also have to recalibrate his TPS after replacing the IAC. I've found that even the black IACs can act very squirrley and need replacement, usually the TPS just needs adjustment

Correct, I had verified that 3 different iac units were functional, that the tps was set, and that I didnt have any vacuum leaks or boost leaks.

And it was a last resort, but ive also never seen it posted besides that this needed to be done with a tech2 tool to monitor the iac functions