Idle surge after running hard

[McB]

I've owned this car for 20 years and barely a problem. Now I've got one that is driving me crazy. Car starts fine, idles fine. When I run it hard, it runs fine, but when I stop, it wont hold idle. The usual scenario - revs go up (air leak?), revs come down (ECU compensates) and sometimes it outright stalls. The thing is, it doesn't happen all the time.

Checked the ICS - resistance good and based on palm logger it's moving fine.
TPS works.
Idle switch good.
Boost gauge shows good vacuum when its holding idle

This whole thing started when I replaced the CAS. Now the CAS works, but there are idle issues.

Just realized my timing is TDC. Could this be the problem?

Anyone?

thanks,

McB!

 

[GsxEcutioner]

I think timing is supposed to be set TDC then insert the CAS with the = on the notch, Maybe you have the CAS turned 180* and then set timing 5*BTDC

 

[steve]

I take it that when you replaced the CAS you didn't set it using a timing light to 5* BTDC.

Keep in mind that the ECU/logger doesn't know that the ISC is actually moving, you can read out what the ECU thinks the ISC steps are but that doesn't mean it really is it's position. The feedback is that the RPMs change when the ECU tries to move the ISC.

Another thing to watch for is that the ISC coils don't go open when it's hot. They can measure good when it's cold but as things expand the winding opens.

What's you idle speed set to?
How much slack in in your throttle cable?
What are your ISC steps when the problem is going on?
Are your coolant lines still connected to the TB like they should be?
When's the last time you replaces the BISS o-ring?

Try bringing the car up to temp and reset the BISS, perhaps it's on the far open end of it's adjustment and when the car gets hot the ECU can't correct any more with the ISC.

 

[McB]

I take it that when you replaced the CAS you didn't set it using a timing light to 5* BTDC.

Will set the timing tomorrow and report back.

Keep in mind that the ECU/logger doesn't know that the ISC is actually moving, you can read out what the ECU thinks the ISC steps are but that doesn't mean it really is it's position. The feedback is that the RPMs change when the ECU tries to move the ISC.

It seems to work during start-up. Will double check as to how it affects RPMs.

Another thing to watch for is that the ISC coils don't go open when it's hot. They can measure good when it's cold but as things expand the winding opens.

Tough one as this is an intermittent. Any thoughts?

What's you idle speed set to?
750
How much slack in in your throttle cable?
Not much
What are your ISC steps when the problem is going on?

Will pull the log file and report back.

Are your coolant lines still connected to the TB like they should be?

Yes, but the EGR has been blocked off for eons.

When's the last time you replaces the BISS o-ring?

Try bringing the car up to temp and reset the BISS, perhaps it's on the far open end of it's adjustment and when the car gets hot the ECU can't correct any more with the ISC.

Will try this.

The BISS o-ring and all of the hoses are original, so the odds of a vacuum leak is quite high. I'll keep looking.

thanks for the input.

McB

 

[steve]

Another thing to watch for is that the ISC coils don't go open when it's hot. They can measure good when it's cold but as things expand the winding opens.

Tough one as this is an intermittent. Any thoughts?

Sure, check them when the problem is happening.

How much slack in in your throttle cable?

Not much

Try adding a little more. As things expand you may be losing the slack and causing the throttle to stay open.

Are your coolant lines still connected to the TB like they should be?

Yes, but the EGR has been blocked off for eons.

Good, but EGR has nothing to do with this. I asked because the FIAV needs the coolant to run through it to close. If it doesn't close the car will surge when hot.

 

[McB]

The car was surging tonight when I stopped. Popped the hood and put my thumb over the BISS. No change. The throttle cable had some slack.
I pulled and and let it snap back and the idle calmed down. Sticky throttle cable?
Throttle plate dirty?
This whole thing started after I had the TB elbow off the car and innards exposed. I'm going to retime/re-idle the car tomorrow. If that doesn't work, I'm going to lube the throttle cable and if still nothing take the elbow back off and look around.

Any other thogughts?

Thanks!

 

[steve]

Sounds like a plan.
Even though you have the EGR blocked you might want to check and see how clean the throttle is. The PCV can still pump a lot of junk into the intake.

 

[eclipse gsx]

my car does the same idk whats the problem i have the egr blocked off and the water lines from the throttle body i just blocked them is this why?

 

[steve]

The water lines are required as long as the FIAV (Fast Idle Air Valve)is connected. With the coolant lines disconnected the FIAV never closes once the car reaches operating temp and it continues to bypass additional air which can cause the car to surge.

 

[McB]

New(er) development.
I got in the car this morning to run an errand. Started fine, but within 5 miles when I stopped at a light, complete stall. Restarted fine. Got to my destination and idle was a mess when I stopped. I turned the A/C on and the RPMs went up and stabilized. Shut the A/C off and the idle was fine at 750. Drove home with no problems. Turned the car off at home, TT kicked in and idle was fine for about 40 seconds then erratic. Cycled the A/C and the idle stabilized at @750.

Correct me if I am wrong, but this sounds like a thermally intermittent ISC, no?

 

[steve]

If you had told me that you measured the coils and found one open when it was hot I'd agree but the symptoms you listed aren't conclusive partially because I'm not sure I know that the idle was a mess and erratic mean.

I've been answered several of these types of questions and getting a little confused as to who's checked what.

If you haven't yet you might want to read the sections on idle in the 1G technical manual you can download from scribe and other places. The links to the FSM and TM are in the DSM FAQ under the TECH menu here.

 

[McB]

By erratic/a mess, I mean idle is jumping around. Still haven't checked the coils hot. Will do when I get a minute.

I've got the the manuals and will look again and see if there is anything helpful there. Didn't get into it today. Overcome by the family...

Thanks,

 

[steve]

Surging up and down or just not stable?

 

[McB]

Not fair to call it a surge, just unstable to a point of often stalling. If I had to guess its the "too much air for a closed throttle-too high of RPM-cut the fuel-repeat syndrome.

 

[Cmele89]

Same thing happens to me, It starts fine runs fine but if i keep it off for about 30 mins and start it up it idles all wierd sometimes it stalls but if i keep the pedal down for a couple seconds it stabilizes... Did u check your idle switch?

 

[GooeyGus]

Check the Idle switch.

My idle gets a bit strange (searches between 1000 and 1100 RPM) when the idle switch is not activated. Mine is intermittent. Sometimes it works, sometimes it doesn't. Although your problem is a bit different, since mine has never tried to stall out.

The idle switch is the switch which the throttle cable bracket makes contact with when it closes. It is very easy to test. With the throttle closed, measure resistance between the terminal on the idle switch and ground. It should be very low. If it tests high or completely open, something isn't right. You can try cleaning it, it worked for me for a couple hundred miles, but I just need a new one.

Also, you should be able to see the value of your idle switch with your logger. I know in TMO it will tell me if it is activated or not.

 

[McB]

Checked the ICS when at op temp. All coils were right around 33ohm. Will reset the timing tomorrow.

Quick question, If I had Cyl. 4 at TDC when I installed the CAS, could that cause this? I'm sure I used Cyl. 1, but now I am starting to second guess myself.

Incidentally, the idle isn't surging as much as going unstable. This only happens at idle. Furthermore, I can make it go away by cycling the A/C on and off.

More tomorrow.

 

[McB]

The timing is now reset to 5* BTDC. Engine certainly runs better, but still the same problem.

The idle is intermittently unstable. The car is fine in open loop (when cold). It seems to act up after it has been run hard. Cycling the A/C on and off will temporary fix it, but once I run for a while it starts going unstable again. When it is stable the idle speed varies between 710 and 760. When unstable in will often stall.

Not sure if any of this new information helps...

Thanks,

Michael

 

[LARRY01Z28]

good info. i still have my idle surge im going to check my tb cable to. thanks guys.

 

[breslin]

...and the latest - Decided to change the PCV valve. In the past, this has caused some minor idle issues. Swapped in a new PCV and the car wouldn't start. Also it was throwing a CEL 13 code (MAF Air Temp). I'm pretty sure a code 13 wouldn't cause the car not to start.

Thoughts?

 

[McB]

...and the latest - Decided to change the PCV valve. In the past, this has caused some minor idle issues. Swapped in a new PCV and the car wouldn't start. Also it was throwing a CEL 13 code (MAF Air Temp). I'm pretty sure a code 13 wouldn't cause the car not to start.

Thoughts?

 

[LARRY01Z28]

what the heck does the pcv valve have to do with starting?? man im getting confused. all i want is my idle surge to go away.

any news??

 

[McB]

Update...

The car will not start. Still showing CEL 13 (air temp sender) and CEL 41 (injector circuit). Remember, the problem started as unsteady idle. This may or may not be related.

Observations:

1) Replaced the MAF and still get the same CEL 13 code. My guess is it's not the ecu.

2) The CEL 41 is "normal" for an F-Con (gotta love HKS). Swapped the F-con with another F-con and still not starting.

3) Palm logger can still talk to the ECU. I did notice that during starting it will disconnect after about a second of cranking. Also the "park neutral switch" light does not change when I press in the clutch. I thought it used to...


So why wont it start?

1) No spark.
2) No fuel.
3) ???

Next steps:

A. Spark
1) I am going to take the f-con out of the "loop." Just one more potential problem...
2) My plugs have about 10K on them. Plan on replacing these.
3) I am running really old Magnecore wires. Will try replacing these.
4) Thoughts?

B. Fuel
1) How can I check this?
2) I have a set of recently cleaned 550s. Would it make sense to swap these in?

I appreciate any help from anyone out there. That Mazdaspeed 3 is looking better all the time...

 

[avengerscoot]

I too have been having the stalling issue....i have checked everything that has been previously posted..all is good and everything is cleaned. My car seems to stall when it gets warmed up. If it doesn't stall it drops low in rpm's. And i'm talking below 500 rpm. At times it comes back up, but only to about 750 to 800 rpm..I too was thinkin it was the BISS screw, but that doesn't seem to be the problem. I have great vacuum and when i pressure tested everything, my little home-made tester...with gauge...stayed still...i am actually lost on this.

 

[McB]

Strangely enough, my problem went away. After the March post of last year, I just let the car sit (frustration abounds). It was, however, hooked up to a battery tender. Sometime around June, I decided to give it a try again. I disconnected the battery tender and hit the ignition and the car would not turn over. After a few component checks, it turns out the battery would charge, but under load would almost completely die. I replaced the battery and...

The car started and ran!!! Not sure what the solution is/was, but it seemed that disconnecting and replace the battery solved the problem. I hope your solution comes as easy.

Good luck.