starting problem

[SVT CAMR]

Ok here is how it goes. Some time the car will not start after warmed up or if it does it will surge in and out and I will have to give it gas to keep it running.

On first initial start in the morning it fires right up. Not sure if this is temperature related or what. I checked code on my scanner and it shows no codes.

Other than that the car runs amazing and smooth. I thought it was just because I hooked up the EGR vacuum line and and the DFPE plug. so I removed all that and put the EGR block off plate back on.

 

[encasedmetal]

iac valve is screwy or throttle is closed too far. it's not fuel or you'd have to completely floor the pedal for it to start

 

[SVT CAMR]

went out like 20 minutes later and it starts! I wonder if it could be a crank position sensor. Should have thrown a code though.

 

[SVT CAMR]

iac valve is screwy or throttle is closed too far. it's not fuel or you'd have to completely floor the pedal for it to start

Thank you I will check them out! Could be throttle closed too far. My idle is around 600-700. What is stock idle?
I checked fuel pressure and it looks normal. I also took the intake pipe off to take a look at the throttle body. Looked good so I just wiped it out with a clean rag. I also checked TPS voltage and it was .981v on my Fluke meter.

 

[SVT CAMR]

I do still have the stock throttle body. I should see if your theory is right.

 

[SVT CAMR]

I ever so slightly bumped up the screw and it seemed to solve the problem. I will know after another longer ride let it sit 10 minutes and it should start. it is idling right at 700-750 rpms right now.

 

[mwolson]

Don't mess with the throttle stop. If you want to check it, log your IACV duty cycle and set the throttle stop so that the IACV duty cycle is 30-35%. But make darned sure you don't have a leak of metered air before you do that.

 

[mwolson]

You should also datalog to make sure that spark is in control of idle. Spark is supposed to be what is doing the fine control of idle, not air. A spark source of 9 indicates spark is in control of idle.

 

[encasedmetal]

You should also datalog to make sure that spark is in control of idle. Spark is supposed to be what is doing the fine control of idle, not air. A spark source of 9 indicates spark is in control of idle.

while I agree with you Mark- his biggest problem is starting not idle. I truly believe he's not getting enough air

 

[SVT CAMR]

Don't mess with the throttle stop. If you want to check it, log your IACV duty cycle and set the throttle stop so that the IACV duty cycle is 30-35%. But make darned sure you don't have a leak of metered air before you do that.

How does one go about this? Will I need special tools? I ask because it is too late… 4 years ago I bumped up the idle screw. I recently put it back by matching the loc-tite on the threads. I then set my TPS to .98v. it was all good!
Then I started installing the stock pulleys along with the AC and a new belt. That is when I noticed the stalling-surging on start up after a short drive then shut down and back out to leave again.

The problem could be fixed already though and I will find out soon but still want to know the procedure of this log duty cycle throttle stop adjustment.

Worst case scenario here is I go up in the attic and install the like new stock throttle body. Right now I have a FRPP Oval Bore that is 12 years old. Never gave me a problem and is still in excellent shape.

 

[mwolson]

Idle is like balancing on a knife edge. It can be really tricky to get right, and you can easily screw it up. Most people don't realize that the PCM uses the IACV to do coarse control of idle but it uses spark to do fine control of idle. When they start changing idle air, due to leaks and/or changing the throttle stop screw, it can really throw the idle off.

If there are no other issues, you can change the throttle stop screw some and it won't throw off your idle, but your IACV will not have the range it has with the stock setting. You can see that in the datalogs for the IACV duty cycle. If it gets lower than 30-35%, it can't cut down on air flow to slow things down. if it gets higher than 35%, it has less headroom for speeding things up.

Encased may be right, and you may get lucky and get your idle to work, but if not, you will need to get access the right tools to get this set up right.

You need access to an SCT handheld or a scanner in order to datalog the things you are trying to fix. I know how to do it with SCT, but have not used a scanner. If you know anyone with an SCT handheld, and they will let you use it, download Livelink from SCT's website and you can datalog all the parameters you will need.

If not, maybe you can find someone local with a scanner who can help you.

 

[SVT CAMR]

Thanks Mark,

That SCT handheld might be the final chapter for my cobra. 2 reasons what you spoke about and to help pass emissions.

With that little tweak I was able to take care of 90% of the problem. Now I barely get a surge on hot start up. It only happened once today. I will see where it goes from here.

Thanks for the advise and insight and recommendations.

BTW you IMRC Relay, PCV oil filter and tweaks to the Dallas speed cal are working great on my car. Thanks Dan.

 

[mwolson]

Glad to help.