My car has been doing this for a while, and it's never really been a huge issue but i'm kind of tired of it now and want to fix it.

I'll start it up, it will idle up a little when cold, then i'll let it sit to warm up, as soon as it gets a little warm, the idle will go from about 1400 rpm drop to 900-1000 for a second until it starts to choke a bit then pop back up to 1400. it will stay there for 4-5 seconds, then go back down, it will just stay on this cycle.

Then once fully warm, and I'm in traffic, if i'm at a light, it will do the same thing, sometimes it feels like its on the verge of stalling, i think it has actually stalled out from this twice now.

From my experience, this seems like a vacuum leak, but I have a single turbo, and there are barely any vacuum lines now, and it did this before it was tuned, and there were no boost leaks when on the dyno.

Sometimes it seems like it happens more often when i push the brakes (still does happen when i don't push the brakes though) could it have something to do with the brake booster system?

Any ideas on what I should do/check first?

 

you can test if it is the brake booster by disconnecting it with the car PARKED and capping the vac line to it. if the idle still goes crazy it is not the booster.

 

is the only line that goes to the break booster the large one that comes off the rear passenger side UIM? A hard line then runs to the booster across the firewall. Just want to make sure I cap the right line.

 

yes

 

Do you have a wideband? Note the A/F at each point. If you have a dataloggit run a log and you can clearly see if it's a rich fluctuation. My car when I pull up to a light bogs and after 5 seconds or so the idle smooths out. I have to spend some time pulling out a little fuel but it's nothing that bothers me too much.

Other than the A/F get some carb cleaner and start spraying away! The brake booster is a good idea to check (I wouldn't have thought to check that one).

If you don't have a dataloggit use the map tracer to see what cells you're using then go over to your injection map and see how the corresponding cells compare.

 

Thanks Lance, my laptop battery died and i need to get a new extension cord, so i wasn't able to plug it in an look at it.

I did however watch the wideband this time. At 1400 rpm, when it sounds pretty normal and even (although probably a bit high) the afr is 12.5-13.0 pretty steady. then when it starts doing its weird cycle up and down, the afr spikes to 16.5 when the rpm drops to 800rpm, it almost shuts off (the gauges actually loose power for a fraction of a second until it catches itself and idles back up. then it just keeps cycling up and down.

On another note, i noticed my oil light came on around 120 degrees F (mid warm up) then shut off when it was ready to go at normal op temp, and never came back on, Any idea on the cause?

 

Your AFR's are going to look weird when it is cycling like that, and won't be that useful. For a 500rpm swing there is either a vacuum issue or something in your idle control.

Since you went single I assume all your extra (now) vacuum ports on the manifold are capped? Try pulling one off to see if anything really changes.

-Andy

 

I remember your car was just tuned, was it doing it then too or did it start after you left Ray?

Assuming no leaks etc there are a few areas in the TEC unit to look at. First try to make sure all the idle cells in the VE table are close to the same milliseconds.

2nd, if your vacuum is changing you can send more control via tps and not the map sensor in the map/blend setting area. I would start with 10% and move up in 10% increments. Since the TPS is stable you get a cleaner idle.

Regarding the breaking up at 7K, do you have the electromotive dual post coils or are they single post? I'll pm you my number, call me and we'll go over some stuff over the phone when you have time.

Anthony

 

You can also try modifying the scaling in the VE table to give you more resolution aroudn the idle area

BTW, are you using the EGO adjustments at all? Sometimes incorrect settings for the EGO correction can flip flop your AFR's.

 

Thanks Anthony, I have the dual post coils. I'll contact you hopefully tonight so we can take a look at the tables.

I don't believe i'm using the EGO adjustments (is that the wideband option?) i don't have the wideband hooked up to the computer, so i haven't done any of the auto tune stuff yet.

 

Yes EGO Correction would be what TEC calls "closed loop". So if your WB02 isn't hooked up its certainly not working

Anthony's bag of tricks should get it sorted though. Namely checking the pulsewidths in the idle cells, and TPS/MAP blend. Out of curiousity, when you say it idles at 1400rpm - is that where you want it to be or where the engine likes to be?

 

I didn't realize you had a TEC. I'd guess your warm up enrichments are not enough. If I run that too lean on my Tec3r it will bog then recover bog recover. If it still does it when fully warm (after your warmup enrichments are zero), then you need to play around with the idle region of the VE table.

How are you doing idle control?

-Andy

 

1400rpm is not really where i'd like the idle to be, and it could be a little lower, it seems like it would run fine around 1100 based on how it sounds when warming up and cold(it idles a little low when cold because i just did the warm up adjustment table myself and it feels good now) when it gets warm it goes up to 1400.

So I think the warmup enrichments are good. Now i just have to focus in on the idle section of the VE as everyone mentioned above. I'll try to get to it tonight, didn't get home from work till 11 last night. I'll also send it to Tony and maybe he'll catch the problem pretty easily.

 

Just remember when you change your idle region of the VE table, it will affect your warm up enrichment curve as well.

When I asked about idle control I meant physically what do you have? Stock idle air control? 4 wire idle air control valve? Just manually set and using Tec to control timing?

-Andy

 

My idle air control wire coming from the TEC is not connected to anything, its just kind of sitting in the engine bay, when i got the car, it was like this, and there is nothing for it to plug into. So i think that means its manually set.

 

Ok, then getting your warm up enrichments and idle VE right is where to start. Getting the warm up curve right can be a pain since car has to be cold to begin with. I'd suggest....

1)Get car warm and play with VE table to get idle smooth
2)Then go back and do warm up enrichment

Just remember anytime you make changes to the idle region VE, it will affect the warm up curve since that adds a % based on VE.


Also check (since you aren't doing idle control) to see if you are using timing to try and hit the idle target RPM. If you are allowing TEC to use a large timing correction to try and hit the target you can get cycling problems as well (timing adjusments are in idle section of the sw I think).

Instead of playing with your idle stop screw and the TB bypass screw alot, I used a manual inline valve (made a line from elbow over to UIM) and that made idle air adjustments easier.

Since there are alot of dependent variables, getting the idle smooth when cold and hot can take awhile. Just be methodical and you'll get there. I wanted more control and purchased the TEC IAC (basically just a GM stepper motor valve) to do idle control. That said, if you can get it to idle smooth manually, it is better to do that before you put on a control valve anway.

My .02.

-Andy

 

Thanks Andy, I will focus on getting it to idle smoothly when warm first, i can't stand being at a stop light fully warm and then having it start cycling and almost dying out in the middle of traffic, How do I tell if timing is being used (i can't open anything on my work computer) would the sw just be 0 if timing is not being used?

 

I have a Tec3R, so not sure your sw version is the same exactly. In the idle control section (from memory) there is a button to select timing advance. If you click that it will let you set how many degrees of timing to add or subtract depending on how many rpm you are off your target idle. For example, you could say add 1deg of timing for every 50rpm you are low, or something like that. While you are getting your mixture right, I'd 0 out the correction so you aren't chasing things.

Good luck with all of this, it can be frustrating and take some time. Power tuning is almost easy compared to getting alot of idle and drivability stuff right.

-Andy