Putting this here to get the prom side of things as everything else has been exhausted.

Trying to tackle an ongoing problem I have with my 86 Iroc converted to SD with a SR on it. It idles perfect when cold, but as it warms it starts to surge, especially after you hit the gas a couple times.(Note if you hit the gas some when cold it will regain it's normal idle.)FYI when you put it in gear it will cut off most of the time, after warm.

It will surge until it gets worse and eventually cuts the car off. It will also surge when the fans kick on.

I have checked almost EVERYTHING and am now looking into the prom. Any suggestions on what to look for in the scan? What values could help with the bad idle. If you hold the idle at or above 1000 manually it is fine. It does seem rich at idle.


I will try to get a scan posted on here tonight


THANK YOU VERY MUCH


Chris

 

I dont know how much tuning u have done, but takes a lot of tweaking some times to get a nice happy idle....

too much or too little fuel at idle tends to make some weird results, especially lean(more surging issues than rich) , or the table where your engine idles(VE or SA) have to great of a change in them and it never finds a happy medium..... IAC working properly and TB clean?

If this is the only thing that u did and now u have this idle issue , i would check the intake and runner gaskets for proper seal, make sure they didnt slip into the engine and/or a warped surface could cause the same as well.......

SR lids are notorious for being warped piles of junk when u try to seal them, a friend of mine had to get anew lid for his(which they will provide if u call and complain)

LAter
Jeremy

 

Watch what your IAC counts are doing.

Once you check for vac leaks for the 10th time, try again. <g>

What for vac line are you running to the MAP sensor?. Copper line is best, and worst is the stock hard plastic. Any rubber neoprene is a no-no.

 

And yes, plenum volume can change the calibration dramatically.
In one experiment I increased it 30%, and had to add 8% fuel at WOT, and lots more AE.

 

Thanks for the help thus far. Skweezn put it on datamaster last night and the BLMs are good 124-127, MAP is around 50 at idle and steady. I am using rubber line(vacuum)The only thing that looks out of place is the is the IAC count is high around 100 and it is hard to get it at anything below 70 before it starts to cut off. Should be around 50 correct?

I did call and get a billet lid and all new gaskets

BTW it is now surging all the time again

Tuning WAS perfect with the LTR setup. I know it will be different now.

I will check vacuum leaks AGAIN More like the 20th time.

Anything else? FYI I am trying a totally different TB tonight



Thanks everybody for the HELP:hail:


Chris

 

First thing to do is trash the rubber line, and replace it with real GM hard plastic, or Copper. The balloning of the hose with fubar your MAP AE.

 

Update: Another tb and IAC did not help at all.

I will change the line ASAP although I am under no boost and had no problems before

Thanks Grumpy

Chris

 

There is no "right" value, but many of us like to keep it as low as possible. The IAC being this high is indicating the motor is needing a lot of air to idle. Instead of relying on the IAC, i suggest you open the TB some more.

suggest you warm the car up to full running temp, then turn OFF all electircal load, headlights, heater, AC, etc... make sure that the motor (really teh alternator) is under the least load possible. this is a condition where the motor needs the least amount of air to run.

THEN, with the scanner hooked up, slowly turn in the "minimum idle" screw (it's the stop screw on the throttle body that controls the minimum closed position of the TB). keep opening it in about 1/4 turn at a time, then wait 5-15 seconds for the idle to stabilize. each time you turn it in (thus opening the TB) the IAC counts go down. My personal opinion is to aim for 5 or 10 under this condition.

 

Update: New MAP and hard line did not fix the problem.

Will check the IAC also and get the counts as low as possible. Maybe tonight will be the night it is fixed. Bad since 10/03



Chris

 

Ive never had much trouble with the rubber lines on NA applications. So long as their rated for vacuum its fine, other types of lines can pinch down on themselves and cause problems.

 

I'm using fuel line for my map. Bad ?? Where would one get copper? I tapped a 1/4 NPT fitting on my intake for the MAP.

I gotta go hunting for a 2-bar map today. The 2-bar I "thought" I had ruined my plugs in about 90 seconds of attempting to idle. OMG, you shoulda seen it Grumpy. Guy standing behind my exhaust was crying.

I assume this was on your boosted car? How did it affect performance ? I have a fully siamesed plenum, and fully siamesed (modified stock, rewelded together) runners. I'm curious if they would perform better than my semi siamese SLPs.

-- Joe

 

If you have done back to back testing in this reguard, then I'd suggest better designed tests, and/or equipment.
I found a difference in my lil 206/206 @ 050 cammed 252.

And there is a difference from not having had any trouble, with testing to find optimum. Which, last time I checked was what tuning was really about.

 

I decided to take a look at it with a low transient response vacuum gauge calibrated in .5 inHg increments. I used a short lenth of hose to jsut mate the end of the gauge up with the vacuum port. Then I used a long length of line. Did some throttle snaps, observed idle, etc.

Know what I found? Its like trying to listen for a whisper in a hurricane. The ammount of vacuum noise from the cam, pcv valve, and other vacuum accesories make it impossible to see any changes. All I can see is noise. At idle the needle is a black blur around 20 inHg with a manic +/- .5 inHg fluctuation. There was also alot of noise from the PCV valve since the rubber line had rotted out inside from all the oil and was acting as a one-way valve. Replaced that and it helped quite things some but any effect would be totally drowned out by all the ambient noise from the engine. Evidently the raw vacuum signal is very noisy from the motor. Really makes me apreciate why the factory included the lag filter for all the fast acting sensors. The lines I use are all thick wall neoprine that yield very little. Probably not much more then a hard plastic line. Id be more worried about the legnth of the line as the column of air can form a standing wave in the line when subjected to excitations. Even that would be hard to pick up with all the noise.

To expand on this further, even with the three feet of line I had hooked up, the needle respnded isntantly to a throttle snap. Followed faster then I could move my hand.

 

We've done a good job of derailing this thread but grumpy, if you could could you post the dia, wall thickness, and material of the line that your using?

 

While you might not see it using a guage, I've seen 10 K/Pa differences in data logged throttle snaps, and had to change the MAP AE, due to changing the hose, with no other changes.

There is alot of difference between looking at a voltage with an O-Scope, vs using a DVM.

 

Where you doing this with boost? Some calcs. show that, fora a naturally aspirated engine, I can expect a worse case senario of at most ~5% change in either of the dimensions of the hose that im using, which equates to around .25% change in per unit volume, if I did the math right. Probably not large enough capacitance to be noticed. On a boosted application, though, the overall changes in dimensions could be as large, or larger then 15% with the same hose if around 2 atmospheres of boost are used.

 

My thread has officially been hijacked!!!


I am learning A LOT though.


The whole intake/including base, is now off of my car.

Chris

 

Nope, just while doing getting off idle AE stuff.
Somethings just don't translate well, into what you see with a calculator.

Under boost it, it threw things off by orders of magnitude. I always post relative to the N/A world, and am specific when I'm referencing to boost.

 

About your test, where both lines the same exact internal dia? Where the lengths the same? Where you using good, thick neoprine lines? I always use the thickest I can find so there is no chance of large changes in dimensions or line pinch-down. There are other variables to consider as well. Air is very compressable and can easily skew results under large changes in pressure over short periods of time. There are also harminic effects to consider as well. Under large excitations air can form standing waves in the line.

As for line, Id use the nylon plastic stuff but in a tight engine compartment that gets hot they quickly harden and shatter easily. Copper would be nice but Id be aftaid of it kinking and breaking when I work on the car. I like rubber the best. High quality line is dead reliable, never breaks, adn can be routed any way I wish. Anyway, those are my preferences and I see you have yours so...

(Man are we off topic, especially on something like vacuum line )