Hey guys, I have a 95' Cobra with a HX-40 Turbo running 12 lbs. Recently I've noticed the car running really shitty at idle. One morning I was driving through town, came to a stop, then my RPM's started fluctuating bad, then the car stalled, tried to crank it back up but it didn't start. Pushed the car into a parking lot then came back to it that afternoon, and it started back up. When I drove back home I let the car idle, then 30 secs later it started the same thing all over again. I changed the ignition coil, IACV, and did a vacuum leak test (no leaks). The car drives great while cruising and under boost. I also noticed from 1k to 2k RPM my car shakes bad. Any advice will help! Thanks guys.
95' Cobra rough idle, stalls sometimes
- Thread starter AlanHam13
- Start date
Have you checked the MAF sensor?
What else is done to the car besides the turbo? What maf? fuel system? Is the car tuned/chipped?
Possibly a TFI module.
I know it has a different maf on it, but not sure what it is. It has a walbro 255 fuel pump with in line boost A pump, 60lb injectors, msd distributor and coil. Then of course forged pistons and h beam rods. The seller said the timing is 8 degrees from top dead center.
That was changed out with the ignition coil.
Problem still exists, recently changed all the plugs, and O2 sensors. Any other suggestions?
Stock distributor? Could be the PIP sensor within the distributor (common thing on the 94-95 cars that goes bad). Use only a Motorcraft replacement part.
It's an MSD distributor. I'll look into the PIP though, thanks.
StockRioRed94
New Member
Hi,
The ECU can remain relatively unchanged during the tuning process at idle for many applications. There exists little difference at low engine speeds between atmospherically aspirated and forcibly inducted engines where positive manifold pressure is not yet present.
This being said, physical components have to be adjusted to ensure the proper operation of the engine. This includes the MAF sensor, injectors, and fuel pump.
I am willing to bet that the transfer function was not properly calibrated when the new MAF was installed. Mass airflow based ECU's are heavily reliant upon input from the MAF. If the sensor output does not correctly reflect reality, engine performance will suffer. You may be thinking, "But it runs fine when cruising." Absolutely, the resolution of the sensor becomes increasingly smaller as engine speed increases due to the little change in actual airflow at high speeds. Engine operation at higher speeds is the easier part to ensure proper operation. Idle, however, is absolutely the most difficult part of engine operation to control.
I would recommend getting the engine tuned and thoroughly looked at. Oh, before I forget. Take a look at the MAF sensor and inspect to see if the mesh screen is still in place. This is an important component to ensure a proper MAF transfer function.
Thanks!
The ECU can remain relatively unchanged during the tuning process at idle for many applications. There exists little difference at low engine speeds between atmospherically aspirated and forcibly inducted engines where positive manifold pressure is not yet present.
This being said, physical components have to be adjusted to ensure the proper operation of the engine. This includes the MAF sensor, injectors, and fuel pump.
I am willing to bet that the transfer function was not properly calibrated when the new MAF was installed. Mass airflow based ECU's are heavily reliant upon input from the MAF. If the sensor output does not correctly reflect reality, engine performance will suffer. You may be thinking, "But it runs fine when cruising." Absolutely, the resolution of the sensor becomes increasingly smaller as engine speed increases due to the little change in actual airflow at high speeds. Engine operation at higher speeds is the easier part to ensure proper operation. Idle, however, is absolutely the most difficult part of engine operation to control.
I would recommend getting the engine tuned and thoroughly looked at. Oh, before I forget. Take a look at the MAF sensor and inspect to see if the mesh screen is still in place. This is an important component to ensure a proper MAF transfer function.
Thanks!
I would say the PIP sensor. I had a problem a while back with my 94 cobra, coming up to a stop and it would just die sometimes. Damn thing would turn over but not start sometimes, cold or hot. Changed TFI module, and ignition coil that didnt help. I just replaced my distributor with a motorcraft original and never had a problem with it again.
Hey thanks for the input, as far as the MAF sensor I didn't actually replace it I just cleaned it. Im currently deployed right now, but my good friend is handling all my fixing needs right now. With that said, should I have him unplug the MAF and start it? To test if it's faulty?
Yeah, it's really annoying! Right now I'm having my friend change the O2's and possibly the MAF... If they both check fine I will move on to the distributor, thanks man!!
Yank that POS MSD dizzy out and throw in a OEM one with a new PIP..
I second that motion. I had to remove a set of their wires last week due to a misfire caused by them.
If he googles the part number on that dizzy he'll literally find more people with problems than ones without. I don't know of any of product with such widespread issues. An OEM dizzy is all you will ever want or need.
I definitely agree with you. As someone else mentioned, as well, check tune status. Rough idle for me has always indicated a lean condition.
Yeah my a/f ratio gauge stays lean at idle, sometimes it doesn't even work (it's a cheap gauge) that's why I'm wondering if maybe it's an O2 issue, but i'll find out here in a few days when they get swapped.
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