Idle Pulsing - what could cause this?

[HartmanMS]

My Talon has been idling poorly for a few days now. It sounds like a V-8 with a big cam. It is like an idle “pulse”. The idle sometimes pulses around 650-850, and sometimes around 900-1000 rpm. When I first start the car, the idle starts high, like normal, at about 1500, dropping down and pulsing a second or two later, with a vacuum of about 8-10mm/Hg. If the car is in gear decelerating, the vacuum drops to 17-18 mm/Hg. This is where the vacuum used to be at idle. I thought it might be a bad EGR, so I blocked it off. I also removed the emissions parts and left all of the solenoids plugged in and capped the ports on the TB. I did this process according to Taboo Speed Shop’s directions. I also checked for vacuum leaks. I was wondering what could cause this odd idle problem. Any ideas? Thanks.

P.S. The car runs pretty rich, but it was running rich before I had this problem...

 

[HartmanMS]

You know, I was thinking today, maybe If I bought some throttle body cleaner at O'Reillys tomorrow, and went through that process, that might help...? Or maybe I should try some MCCC? What do you guys think I could do to try to fix this problem? I really want to get the Talon running right again. Thanks!

 

[V8HAHA]

We just fixed this on my buddy's GSX. We did a leak test and found quite a major leak. It was the vacuum line going fro the intake manifold to the FPR, there was a stress crack in the line where it connected to the intake manifold. As soon as we fixed this, the problem was resolved. Anywho, just do a leakdown test and fix any leaks. The smallest leak can cause a big problem. If there are no leaks, it is probably the ISC.

EDIT: I just read that you did a leak-down test. Make sure you did it at the same PSI your running.

 

[HartmanMS]

Well, a "leak-down" test, is when you pump air into the cylinder at top dead center to see if air leaks into your intake, exhaust, coolant or crankcase. I haven't done that. I have just watched my boost gauge at idle and it reads low. I might see if I can rent a vacuum pump to check for leaks taht way. It just doesn't make since to me that the vacuum would return to normal with a load on the motor, in gear, decelerating...
ill try again to check for vacuum leaks though.

 

[2.4 turbo Hyped]

A boost leak test would be a good start to this situation. Thats where I would start at least. Id then check my ohmage output on the coils of the isc.

 

[HartmanMS]

What SHOULD the resistance of the isc coils be if the vacuum test shows nothing? And how exactly do you test them?

 

[2.4 turbo Hyped]

What SHOULD the resistance of the isc coils be if the vacuum test shows nothing? And how exactly do you test them?

I said a boost leak test not a vacuum test. Anyhow, testing your isc is on vfaq.com or plymouthlaser.com

 

[V8HAHA]

Well, a "leak-down" test, is when you pump air into the cylinder at top dead center to see if air leaks into your intake, exhaust, coolant or crankcase. I haven't done that. I have just watched my boost gauge at idle and it reads low. I might see if I can rent a vacuum pump to check for leaks taht way. It just doesn't make since to me that the vacuum would return to normal with a load on the motor, in gear, decelerating...
ill try again to check for vacuum leaks though.

Sorry my mistake, that is what I meant, wrong wording . resistance of the pins on the ISC should be between 28-33 ohms.

 

[HartmanMS]

I don't really think a boost leak would be the issue, since I have no problems on the upper end, and boost is steady, but I'll give that a shot too. That's why I am going to do a vacuum leak test. I will do all of the above though, it can't hurt...

 

[HartmanMS]

I tested my isc prongs 1-2, 2-3, 4-5, and 5-6. They all read right at 42 ohms. This is the site i ended up using for procedure and tolerances
DSM Test Page The tolerances were to be between 36-46. My isc checks good. I am going to go do a comp. test now. ill get those numbers posted in an hour or so.

 

[HartmanMS]

I did the compression test. pass. side to driver's side, (cyl. 4-3-2-1, I beleive.) The numbers were: 175-150-150-158 What do you guys think? Service limit is 133, so no cylinder is that low, but there is considerable variation, does that mean anything conclusive? Thanks again guys for helping me with this.

 

[91talonontsi]

how do you perform a vacum test on a car. because its not my talon but i have a 1992 taurus SHO and it runs like pooo... ive tried everthing to make it work right but i have never even thought about having little or no vacum. so can this be done with no speical tools????

 

[HartmanMS]

You tee into a vacuum source from the manifold and pump the vacuum pump to about 20psi or so and then listen for hissing leaks. You really should have started a new thread instead of posting in this one, but, now you know.

 

[HartmanMS]

I know how easy it can be to get the timing belt off one notch on our 4g63's, so tomorrow I will take the digital camera and take some pictures, of my cam gears with a straight edge, and the crank pulley on its tdc mark. Maybe you guys can help me verify that it is dead on or...hopefully not...off a tooth. (after i changed it twice)I don't know what else to try, until i can get a vacuum tester that WORKS...

 

[V8HAHA]

The resistance between each of the pins on isc is suppose to be 28-33 ohms, unless i'm reading the link you posted wrong.

 

[HartmanMS]

You're right I completely skipped over that. These are the correct 2G isc spec numbers too, right? Can anyone verify that? It was also only 35-40 degrees yesterday...how much would that affect it?

 

[V8HAHA]

seeing how the ISC on 1Gs and 2Gs are interchangable, i would assume that doesn't matter (don't quote me, but I think this is true). If your concerned about the temperature thing, maybe heat up the throttlebody assembly up with a heat gun a little and try it then?

 

[HartmanMS]

I took some pictures of how my timing is aligned. This looks good to me, what do you guys think?

Hope these pictures work

 

[V8HAHA]

looks good to me. To be sure, you can run that ruler all the way across to the other side of each cam gear... there are 4 marks. Also, I could be wrong, but it looks like your timing isn't set to 5* advanced.

 

[blue92laser]

Ehm, you need a timing lite to see where your timing is advanced, oh yeh, and the motor has to be running. Hmm....

Looks like the MECHANICAL part is fine, try setting the IGNITION TIMING with a gun, see if it is zeroed out, I know mine was zeroed out and I have no idea why still, but I readvanced it to 5 degrees and it doesnt surge anymore. Try it, nothing to lose.

 

[HartmanMS]

Well, I can get a timing light, but I was under the impression that the ignition timing advance/retard is completely controlled by the ECU and not adjustable on a 2G DSM. Couldn't I just hook up my logger and check the timing at idle with that? That will give the same readings as a timing light I believe.


I went ahead and checked the idle timing before submitting this post. My timing at idle bounces erratically anywhere from 3-4*, to about 18-19*... its timing seems to be jumping up and down just like its idle.

 

[blue92laser]

Well, I didn't realize you had a 2g car. Hmm, your timings jumping? Well, mine was doing the same thing. I replaced the caps on the ECU and the cam position sensor, but I have a 1g....I am not two familiar with 2g's. Try it though. It may work.

 

[HartmanMS]

Well, I could very well be wrong, but I think the 95-96 DSMs run the ignition timing off of the CRANK ANGLE SENSOR, and the 97-99 ran it off of a CAM ANGLE SENSOR...correct me if I am wrong. How could I test that sensor?

 

[The Foos]

If it idles "loopy" only when the engine is up to temperature, check the coolant temperature sensor. This sensor is one of the components that tells your ECU which map to run off of, and if it is bad, it can take you rich or lean. Then you o2 sensor compensates; well you can see the pattern.

Scott

 

[HartmanMS]

It idles crappy like this constantly; cold and warm. Once I floor it, it's fine. In the high rpm's at part throttle its fine. It seems to be only an idle problem...