06blackAT

Looking for some help,

-Was driving on the highway the other day, decided to arm my zex system to pass a big rig. Shortly after I let off the gas and disarmed the system I noticed my car seemed jumpy and the CEL started to flash. I pulled over to the side of the road and the car stalled. When I opened the hood I noticed that although the nitrous management unit was off, nitrous was still pouring into the UIM. I closed the bottle, waited for 30 mins and went to start the car.... clearly there was residual nitrous in the UIM because it violently exploded.

My new UIM came in today and I cleaned out all the shards of old UIM and installed the new piece. When I started the car the idle shot up to 4k and stayed there for about a minute. Instead of dropping down and stabilizing, It seems the CPU is bouncing the idle between 3k-3500. Its not un-commanded erratic idle changes, it looks and sounds programmed.

Any ideas what could be causing this?

More info on my car:

2006 6 port A/T
2nd motor
120,000 miles

RIWWP

iTrader: (2)

Yes, the problem is that you exploded your UIM from nitrous use

It's not a common problem, but it is typical on using the nitrous too early in the rev range, and particularly more of a problem for automatic transmission equipped RX-8.

You aren't the first, one guy blew them up on a regular basis, mostly from stubborness: https://www.rx8club.com/rx-8-multime...nifold-165813/

RIWWP

iTrader: (2)

Oh, causing the idle issue on the new manifold...

If you can control the revs above that point with the pedal still, then the issue is probably that you have a lot of excess air flowing into the engine, so it fuels accordingly and the revs stay high.

If the pedal does not respond, then it is in a limp mode because it knows something is wrong and can't figure out what that is, so it has disabled the pedal's input to prevent you from controlling the throttle body.

06blackAT

I have control over the TB, so there must be extra air getting into the motor.

Oh and my particular exploding UIM was more like a turn-key car bomb, I never sprayed under 4k rpm

RIWWP

iTrader: (2)

Clear your fuel trims, then check them at idle. If they are hugely positive, then you have a massive vacuum leak somewhere.
Basically, a vacuum leak is air getting to the engine that isn't passing the MAF, which by itself would just mean hugely lean, but the O2 will see that and start adding the needed fuel, which the engine will respond to and the revs will increase substantially, more than the idle air control can solve for to reduce.


If the trims are zero and your AFRs are normal, then you probably have a throttle body problem where it can't close properly, so all the air is flowing through "normally" and the ECU isn't really aware of the problem.

I bet it's the former though, since we have so many checks against proper throttle body operation.

9krpmrx8

iTrader: (46)

Fuel pooling is bad mmmkay.

06blackAT

Is the throttle body supposed to be slightly open at the bottom in its closed position?

RIWWP

iTrader: (2)

Yes, though "slightly" probably needs a more precise measurement, in case we think you mean half a millimeter and you mean half an inch.

06blackAT

I actually think the plate in the throttle body may be bent. My car was off when the explosion occurred, meaning the throttle body was closed... the explosion may have bent the TB.

RIWWP

iTrader: (2)

That could certainly do it. The ECU thinks it's closed, but it's still enough flow for 3,500rpm at idle...

And the throttle plate isn't designed to take an explosive force from the downstream side....

06blackAT

Well, found out that vacuum solenoid KL01 18 74(one of the three that are under the oil fill part of the UIM) had sheared off from the tube it was connected to.

Ordered the part, going to see if that was the problem.

RIWWP

iTrader: (2)

Yeah. Basically every internal surface that sees vacuum normally, a mild pulling motion, got a sharp pushing blast, and could be damaged. Solenoids, valving, sensors, manifold hardware, gaskets, seals, etc...

Easy_E1

iTrader: (2)

Stubbornness? Oh come on RIWWP. I was testing. I had to find the edge of the envelope. lol

More than likely you have a bent throttle body butterfly. I bent one once.

RIWWP

iTrader: (2)