wstrohm

1994 FD, stock except for Bonez downpipe, 88K miles. Gas mileage about 13-14 mpg city, about 20-21 on road. When warm, vacuum at 700 rpm idle is about 17 - 18 in (Hg). Good power at WOT, very smooth cruising. No stored ECU fault codes. Plugs are stock (non-platinum) NGKs, replaced about 100 miles ago. Plug wires are on the 2nd set since car was new (we are the original owners). The catalytic converter was replaced with an OEM in 2002.

Recently, the exhaust when engine is cold has started smelling very rich, along with some oil smoke which goes away when warm. When first started, the idle is fast, but rough. As the engine warms up, the idle speed comes down, but missing can be felt from inside the car. When fully warm, the idle tends to "hang up" around 1000 - 1100 rpm for sometimes the full length of a traffic light, and sometimes will drop back down to a steady 700 rpm fairly promptly. Whether at 1 K rpm or 700 rpm, occasional missing is evident. I would guess a vacuum leak, if the Mity-Vac reading weren't so steady.

Fairly recently, I replaced all the original vacuum hoses with Viton 1/8" and 1/4" ID sizes. The 1/8" hoses are all quite tight, but the 1/4" hoses were just a tad large, and I had to tie-wrap them on several connections. This problem did NOT surface immediately after the hose job.

Any suggestions?

kraked

I have the same problem too--I even took it in to have it looked at but they couldn't determine the cause. I am suspecting that my cat may be starting to fail.

dgeesaman

iTrader: (7)

Did you get your injectors cleaned and tested during the hose job? IMO it's always worth doing on original injectors when you have the opportunity.

kraked

My car did the same thing as wstrohm and I just pulled the injectors for cleaning. Turns out, my spray pattern and flow rate was only about 3-6 percent improved--had good clean injectors even before sending them out.

wstrohm

dgeesaman,

Negative, I did not touch anything more than absolutely necessary to do the hose job, and trust me, that was enough! I hear you, though. I am a Techron fan and periodically add their Fuel System Cleaner before pumping gas. Just did that, as a matter of fact, to our last $54 tankful... no difference so far.

wstrohm

Well, I still have the same problem as in my original post of 2006, here in March of 2008! There are no stored fault codes. I checked the "High idle speed after warm-up" (page F-209 of my '94 FWM), and it lists 6 possibilities, each of which I have checked out. The fast idle cam isn't the problem, because the idle will drop down sometimes, and speed up other times... I don't think the cam can go both directions randomly, and the wax thermostat operates normally. The AWS valve solenoid coil measured 13.0 ohms whereas the spec is 9.3 - 11.3 ohms, so I guess that is a possibility, but seems unlikely, and the action of its valve is smooth. The IAC valve coil measures 12.1 ohms, spec is 10.7 - 12.3 ohms, so that's OK, and it operates smoothly also. The voltages on the engine coolant temperature sensor are correct at cold and hot, i.e. 2.2 volts cold and 0.5 volts hot. There is plenty of slack in the throttle cable at idle, and the dashpot is also adjusted correctly and operates smoothly. I just installed a new OEM PCV valve; no difference. Plugs are fairly new and stock, plug wires are also new, knock sensor is new, TPS is adjusted and all voltages are in spec, MAP sensor voltage vs. vacuum/boost is in spec.

The odd thing is that when the idle speed is 750 rpm, where I set it, the engine idles smoothly. But when it is idling at the higher rpm (1200 - 1400), there is a definite miss, like a vacuum leak. But the MityVac says vacuum is steady for either "state" of the idle. I can't understand what would cause both an increase in idle speed and a simultaneous miss.

Any thoughts?

NCMontegott

iTrader: (5)

i have had the same problem for a while, i have done all the test that you have done to no avail. the only thing that i could think it is would be a lim gasket that needs to be replaced since it would be unaccounted air in the system after the map sensor. hope this helps.

wstrohm

Thanks for your input. Is it possible for a gasket to leak intermittently? Seal-no seal randomly? That would be a new one on me.

arghx

iTrader: (3)

You can try a boost/vacuum leak tester to see if there is some random leak that you missed. www.boostpro.net/prodtester.html . I have never used it on an FD with a stock airbox, but I think you want the "dual pop" one. Worth a shot anyway. Myself and many other owners have had great success with these kind of testers on single turbo applications.

wstrohm

arghx,

Thanks, but I don't have an air compressor except for a tire air compressor, which does not have the volume capability to pressurize an entire intake system. I do have vacuum gauges, though.

NTIMD8

iTrader: (1)

My car does the exact same thing as you described in your first post. Doesnt bother me much since it is so subtle and then once warm it doesnt have the slight miss that it has every little bit when cold. If oyu find out the cause I would love to hear it.

Monsterbox

iTrader: (6)

my fd does the same thing...until it hits exactly 140f

if I pull out the fuel on the PFS Purple Box under 140F at idle it will run completely normal and then stall at 140F...this obviously means that the car is ramping the fuel on its own as some kind of cold start compensation but more like an overcomp.

I just let it do its thing...

supraturbo1987

iTrader: (4)

I just found this post. I have a motor with 1500 miles on it with the stock emissions deleted, airpump unhooked, gutted cat, stock intake, DP, catback and simplified sequential twins. My car is pretty rough when warming on a cold start for the first 5 minutes, then the idle lowers and it gets a little quieter. Sometimes when I come to a stop, the idle is between 1000 and 1500 and is missing and sometimes is it at 750-900 and running fairly smooth. I just figured it had something to do with the emissions delete, but there must be a fix if basically stock cars are doing the same thing....I am on a stock ECU

Trev

wstrohm

I checked intake manifold vacuum today with car fully warm, and it sat at a solid 17" (Hg) on my MityVac whether the idle was at 720 rpm or 1300 rpm. Still scratching my head over this issue.

wstrohm

Just for drill, I pulled the MityVac hose off the normally plugged vacuum tap on the passenger side of the UIM, where I measured vacuum (in my previous post). The idle jumped up yet higher, and the missing became more pronounced. Putting the cap back on the tap reversed the effect. So now I think there is a vacuum leak somewhere that just randomly comes and goes. Don't have any idea how to find it.

wstrohm

How do you delete a duplicate post? Can't find a "Delete" icon!!!!

wstrohm

Car now has 96K miles on it, and just barely passed CA smog testing today. Worst case was a measured CO of 0.52% @ 15 mph (1795 rpm), which is the maximum allowable value. HC was at 74 ppm; spec is <= 88 ppm @ 15 mph. Both numbers improved somewhat at 25 mph (2869 rpm). The idle is as I have described it in my previous posts in this thread. So I have the following questions:

1) Doesn't the MAP sensor read the total overall absolute pressure (vacuum) in the intake manifold including UIM and LIM? It is all one big volume, correct?

2) If answer to 1) is "yes," how does any intake air leak cause missing, since the MAP sensor should just increase fuel as manifold pressure goes up, to keep A/F ratio at the right value? Shouldn't the idle just increase due to an air leak, and not start missing?

3) if I put my MityVac on the "load" side of the vacuum chamber, i.e. remove the output hose from the chamber and hook it up to the output hose, with engine off, should it be able to pull a vacuum and hold it for a reasonable length of time if everything is not leaking? Or is there going to be an open solenoid or other air path even if everything is normal?

I'd appreciate any inputs you experts might have on this problem! Thanks!

NCMontegott

iTrader: (5)

1) Doesn't the MAP sensor read the total overall absolute pressure (vacuum) in the intake manifold including UIM and LIM? It is all one big volume, correct?

no it ony reads at the point at where the map sensor is connected at the uim right next to the TB

2) If answer to 1) is "yes," how does any intake air leak cause missing, since the MAP sensor should just increase fuel as manifold pressure goes up, to keep A/F ratio at the right value? Shouldn't the idle just increase due to an air leak, and not start missing?

What happens when you turn the car on, before the engine rotates the map sensor/ecu takes a reading of the barometric pressure ie ( atmospheric pressure) and the car calculates the ammount of fuel needed for the engine to run. now im not sure if it can constantly recalculate while dirving? but i would think that the car cant because of the forced induction of the fd, so the atmospheric pressure would not matter. the problem is most likely as in my car is a vac leak after the map sensor, so the ecu can not adjust for the vac leak, im going to buy the vac/pressure tester sold by fighters garage, and hopefully I can find the leak.
hope this helps.

Adam

gracer7-rx7

iTrader: (16)

I believe it is just one big volume since there are no separations.



I'd also like to know that...


Are you running the later metal UIM to LIM gasket? Have you checked for other air leaks at the TB and such?

Also have you checked your coils? I've heard they get bad with time and heat.

The only other thing I can think of is a possible problem with the air injection from the air pump to the motor and cat

wstrohm

Yes.No; don't know how to do that... gaskets seem secure, bolts are torqued to spec, do you have ideas how to do that?Have only tested coil resistances per the manual. Under load, i.e. accelerating or climbing hills, there is no stumbling or missing. Am I correct that the high voltage section of the ignition system would tend to fail under load if the idle problem is the coils?The secondary air pump injects air after combustion, into the exhaust ports and cat converter... how could it affect idling?

My question 2) above is the one to which I would really like an answer. I am used to air flow meters, mass air flow sensors, etc, which measure the incoming air flow and send a signal to the PCME to control the fuel injector pulse widths. So in those cases, the intake manifold getting un-metered outside air will cause lean A/F mixture, and missing. But the MAP sensor doesn't really care where the air comes from (does it?). It just measures the air pressure in the intake manifold and adjusts the fuel pulse widths to give the correct A/F ratio. So how can a vacuum leak cause anything other than a rise in engine speed? (Of course, that is the other thing I'm getting...)

gracer7-rx7

iTrader: (16)

I guess what I was really suggesting was whether you checked the condition of the stock gaskets. Which I would have assumed you did.


I would think that if there were a problem with the coils, it would most noticeably present itself under high load and/or high heat situations. I would think that it would be difficult to feel the effects of a slightly out of spec coil problem under normal use but I speculate that an out of spec coil may have some slight affect at other running conditions besides full load at high RPM and boost - possibly an effect similar to yours.

I also have a slight miss and I my last dyno session leads me to believe that my 135k mile coils need to be tested and probably replaced.

Sorry but I haven't done enough research on this yet to answer your question. I could be totally off in suggesting it but the reason I mentioned it is b/c when I connect the electric plug to my airpump, my car idle rises slightly and it feels like it starts to miss and pop a little. My PFC isn't tuned to work with the airpump right now.

Hopefully someone more knowledgeable can offer further info on that if appropriate.

Yep. Totally agree with that. The only other place to get unmetered air is potentially from the airpump.

Agreed here also.

userjh5174

Try testing the Trottle Position Sensor (TPS).
Dion

gracer7-rx7

iTrader: (16)

^ he did

Dusted RX

Have you adjusted the idle air screw at the base of the throttle body? When switching from stock ECU to PFC this needs to be done to get the idle to work properly. In the factory position it is about 10 turns open, but should be adjusted to about only half a turn out.

wstrohm

Yes, that adjustment will take me above and below the desired 720 rpm when engine is warm. I set it so that idle speed is the same either with the "TEN" - "GND" jumper in, or out. And sometimes the idle goes right to that point. But sometimes it doesn't, instead staying at 1200 - 1300 rpm, say at the next traffic light. And then back again later to the place I set it. But the idle is rough... a lot of "putt-putts" when the idle is up; lately also when it is at the right rpm.