Weird idle problem

WhiteThunder

WhiteThunder

Registered User
Well, maybe it's not so weird. Did a search and didn’t find this one right off …

I have a ‘90 5-speed SC. Weekend car. Just added a Kenny Wagner double intercooler (He does great work).

After installing the double IC, the car idled fine. But, when I took the car on the street, each time I put the clutch in for a red light and such, the rpm’s would swing wildly from about nothing to 2,500. Many times the car would stall.

After driving it a few more times, the problem has become intermittent. When stopping, the idle will sometimes swing from about nothing to around 1,500 rpm. Other times it idles just fine. Sometimes when stopped it idles where it was set when tuned, at 800 rpm, but will idle rough. Other times it idles smoothly.

I’m using Texas Thunderbird IC gaskets. IC tubes and spanner nut are very tight. I’m getting 18.5 lbs of boost at full throttle – same as before the double IC. Cam is .519 (.300 lobe lift 284/224 duration).

Got solid motor mounts. They’re about as new as the rebuilt engine – around 10,000 miles.

Any ideas? IAC (a couple of years old) going bad?

eddie
'90 5-speed SC
'97 LX sport
 
Sounds like a vacuum leak. Spray the IC tube connections with carbor brake cleaner while it's running to locate leaks.

David
 
When did the idle start acting up?..After IC install or before?

If not a vacuum leak your cam may require your idle to be raised
 
After

DamonSlowpokeBaumann said:
When did the idle start acting up?..After IC install or before?

If not a vacuum leak your cam may require your idle to be raised
Click to expand...


It started acting up after the double IC install.

I had the idle raised after the cam because I was having stall problems with the a/c on.

I'll test it with brake cleaner and/or carb cleaner this weekend.

I did check the tightness of the IC tube nuts last night - the lower nut on the upper end on the return tube took a quarter turn. The spanner nut turned a hair.

I didn't think there was a vacuum draw on the IC tubes at idle. Wouldn't the only vacuum draw at idle be at the throttle body and intake plenum?

eddie
'90 5-speed SC
'97 LX sport
 
WhiteThunder said:
I didn't think there was a vacuum draw on the IC tubes at idle. Wouldn't the only vacuum draw at idle be at the throttle body and intake plenum?

eddie
'90 5-speed SC
'97 LX sport
Click to expand...

Nope..Anything after the TB will need to hold vacuum (includes IC tubes, IC, SC top, return plenum). Everything after the supercharger outlet will have to hold vacuum and boost. It doesn't take much of a leak to make it run like crap.

David
 
thanks

David Neibert said:
Nope..Anything after the TB will need to hold vacuum (includes IC tubes, IC, SC top, return plenum). Everything after the supercharger outlet will have to hold vacuum and boost. It doesn't take much of a leak to make it run like crap.

David
Click to expand...


Thanks.

Since the problem started after installing the double IC, this weekend I'll change the IC gaskets. Maybe the one at the spanner nut didn't seat correctly. A good while back I did change one of those gaskets because it cracked and split.

eddie
'90 5-speed SC
'97 LX sport
 
WhiteThunder said:
Thanks.

Since the problem started after installing the double IC, this weekend I'll change the IC gaskets. Maybe the one at the spanner nut didn't seat correctly. A good while back I did change one of those gaskets because it cracked and split.

eddie
'90 5-speed SC
'97 LX sport
Click to expand...

Eddie,

If you don't have a spare gasket, Permatex Copper RTV work well too.

David
 
Have a set

David Neibert said:
Eddie,

If you don't have a spare gasket, Permatex Copper RTV work well too.

David
Click to expand...


David,

Thank you for the offer. I have a new set of those teflon IC gaskets that I purchased from a SCCOA member. I should have changed them when I switched to the double IC instead of clamping down hard on the old gaskets.

eddie
'90 5-speed SC
'97 LX sport
 
Most likely it is vaccum related....can you give a vaccum reading with your car at idle (when it's not reving irradically). With your cam and being 5 speed I would think something at 20 inches (give or take an inch) should be what you see.

Otherwise, if your TPS voltage is set over 1.00 volt at idle, you will have a similar problem with rpms surging up to about 2500 rpm and back down. Since most TPS's are set at .90-.95+ it's not too hard to whack the thing and send it over the 1.00 mark. You can easily check your voltage with a paper clip and a voltmeter.
 
I had a vacuum leak on my car that made it run horrible unless I was going wide open throttle. When I could keep it running at idle (surging up and down) the vacuum gauge readings were normal, so the leak might not show up on the gauge.

David
 
mywhite89 said:
Make sure to check the double intercooler itself. I've heard of those having problems with leaks.
Click to expand...

If it came from anyone but Ken Wagner, I would agree. Ken does a good job of sealing them up and I'm sure he test them for leaks prior to shipping.

David
 
This weekend

Thanks for all the replies.

With the cam I have, my Autometer vacuum gauge reads around 10 at idle - same as it did before the double IC and when I had the stock gauge in the dash.

I'll change the IC tube gaskets this Saturday. I'm guessing that one of the IC gaskets cracked or the IC gasket at the spanner nut slipped down and didn't seat correctly during assembly.

If the new teflon IC gaskets I have do not solve the problem, I'll check the IC and/or change the TPS.

I have a multimeter to check the TPS voltage. Do you pull the plug and check it at the plug while the car is running? Or do you tap into the wire going to the plug and check the voltage while the engine idles?

Never a dull moment with the SC.

I'll keep y'all posted.

eddie
'90 5-speed SC
'97 LX sport
 
WhiteThunder said:
Thanks for all the replies.

With the cam I have, my Autometer vacuum gauge reads around 10 at idle - same as it did before the double IC and when I had the stock gauge in the dash.

I'll change the IC tube gaskets this Saturday. I'm guessing that one of the IC gaskets cracked or the IC gasket at the spanner nut slipped down and didn't seat correctly during assembly.

If the new teflon IC gaskets I have do not solve the problem, I'll check the IC and/or change the TPS.

I have a multimeter to check the TPS voltage. Do you pull the plug and check it at the plug while the car is running? Or do you tap into the wire going to the plug and check the voltage while the engine idles?

Never a dull moment with the SC.

I'll keep y'all posted.

eddie
'90 5-speed SC
'97 LX sport
Click to expand...

Eddie,

Tap into the wiring for taking the TPS voltage readings....easist way to tap into the wire, is to push a straight pin into it and take your readings off the body of the pin.

David
 
Last edited:
Or the paper clip...just straighten one leg of it and slip it into the pin (where the wires come out of your harness). I think you tap the green wire for positive and then just find a ground somewhere.

BTW, 10 inches sounds REALLY low. I have a 509 lift cam with 208 duration on intake and exhaust and pulled 18-20 regularly. I can't tell what your actual duration is 224/224?, but I would think you should be seeing well over 10 on a five speed. (15 sounds better).
 
vacuum

Micahdogg said:
Or the paper clip...just straighten one leg of it and slip it into the pin (where the wires come out of your harness). I think you tap the green wire for positive and then just find a ground somewhere.

BTW, 10 inches sounds REALLY low. I have a 509 lift cam with 208 duration on intake and exhaust and pulled 18-20 regularly. I can't tell what your actual duration is 224/224?, but I would think you should be seeing well over 10 on a five speed. (15 sounds better).
Click to expand...

My cam is .519 (.300 lobe lift 284/224 duration - 1.8 roller rockers giving it a
.540 lift). The car had 10 inches of vacuum when I started it up after the
1st rebuild (it threw a rod). And it had the same after the 2nd rebuild (dropped a valve). The engine has a very noticeable lope.

I need a good tune. The guy I used here in South Florida is AWOL. Dave Dalke needs to come around.

eddie
'90 5-speed SC
'97 LX sport
 
WhiteThunder said:
My cam is .519 (.300 lobe lift 284/224 duration - 1.8 roller rockers giving it a
.540 lift). The car had 10 inches of vacuum when I started it up after the
1st rebuild (it threw a rod). And it had the same after the 2nd rebuild (dropped a valve). The engine has a very noticeable lope.

I need a good tune. The guy I used here in South Florida is AWOL. Dave Dalke needs to come around.

eddie
'90 5-speed SC
'97 LX sport
Click to expand...

just curious here.. (seeing as im from Ft.Lauderdale), who are you using for a tune?
 
Good South Florida SC tuner?

Blown 91 Bird said:
just curious here.. (seeing as im from Ft.Lauderdale), who are you using for a tune?
Click to expand...

Last couple of times I used Dan Rotolante of Accelerated Technologies. He was down in the Kendall area. His Website is gone and cell phone disconnected.

Last time I had it tuned the supercharger belt was slipping badly. Since then I've had the supercharger ported, 15% MP overdrive pulley combo and the double IC added.

Do you know someone down here that's good?

eddie
'90 5-speed SC
'97 LX sport
 
that knows supercoupes... no. When Jerry was with superchips thats who everyone pretty much used for stock ecm cars.

I always used Stephan at Cartek (in the warehouses off of 84 just east of Univirsity Drive) for dyno time, but did my own tuning. Only other reliable dyno facility i would go to is Mustang Specialties up in pompano, but not sure if they can do anything with the supercoupe or not.
 
Blown 91 Bird said:
that knows supercoupes... no. When Jerry was with superchips thats who everyone pretty much used for stock ecm cars.

I always used Stephan at Cartek (in the warehouses off of 84 just east of Univirsity Drive) for dyno time, but did my own tuning. Only other reliable dyno facility i would go to is Mustang Specialties up in pompano, but not sure if they can do anything with the supercoupe or not.
Click to expand...

Well, it's an EEC-IV, just like the 5.0's had, so I'm sure you can get into it with whatever they use.
 
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