Run Rich and Idle hunt problem ECUTALK!

[good2go240]

UPDATE: I bought the ecu talk program and now have some data....the egr is opening randomly at idle and thats when my car will hunt bad and then die. anyone able to explain this for me? I can send you my excel spread sheets unless someone can tell me how to put them on here. im getting about 15 miles to the gallon and just replaced the knock sensor. replaced the bad ohmed injector but have yet to pull rail to see if it is actually leaking.


Ok i am a 2nd year student at a community college in the automotive program. I have a 1991 nissan 240sx HB 5 speed with the ka24de 170k miles.
I have searched and cant seem to find a problem similar to mine.

Problem:
Car starts up and and idles high about 1000 and then after running for a few minutes every 20 seconds it will rev slightly higher 1300 and then drop to almost 200 then back up to about 1000 and down to 200-0 times for a 6 second period. Sometimes it will completely die. It runs very rich the whole time and it gets terrible gas mileage. randomly my check engine light will briefly come on when stepping on the accelerator but quickly disappears when let off. I check the ecu via the blinking light and it recently only gives me code 55
but before i reset the computer i had a leaky fuel injector (california) and knock sensor, but those have not reappeared.

Attempts to diagnose:
Resistance and voltage tested sensors MAF and 02
Power balance test (fine)
pulled off maf and car idles different and wont rev past 2500
pinch main hose going to iacv and idle wants to die
pull off coolant temp sensor and it dies


Dry Compression test
cyl 1: 160
cyl 2: 160
Cyl 3:150
cyl 4: 155

Wet Compression Test
cyl 1 180
cyl 2 175
cyl 3 175
cyl 4 170

Smoke tested for vacuum leaks and nothing appeared leaking

Replaced:
Spark plugs and wires
cap and rotor
maf
o2 sensor
fuel pressure regulator

Removed and cleaned IACV and seafoamed engine via brake booster vacuum

Engine Performance modifications:
walbro 255 fuel pump
Aem cold air intake
electric fan
Optima yellowtop

Could it be egr? im running out of ideas

If im missing anything please let me know, Im dieing to figure this out. Thank you!

[Razi]

Do you have the FSM?
If you don't, I highly suggest downloading them all onto a folder.
http://www.nicoclub.com/FSM/240sx/91-94/
EF & EC
There are diagnoses for an idle that hunts or is unstable on the EF & EC section, starting at page 59.

I think out of all the tests it lists, the only one you might've not done is checking the EGR, so I'd make sure that's functioning properly.

[mechanicalmoron]

Make sure your TPS is adjusted properly.

It will cause rough idle, high or low idle, surging idle, dieing at stops, etc.

And then, after you have the TPS done, properly (with unplugging the tps) set the iacv.

[blackandblue]

bump TPS

[good2go240]

anyone?

[mechanicalmoron]

anyone?

TPS.

Possibly temp sensor? dunno.

TPS.

Just check the thing.

[good2go240]

checked the tps and it was at .50. adjusted to .45 and still same problem is happening

[mechanicalmoron]

checked the tps and it was at .50. adjusted to .45 and still same problem is happening

.44

temp sensor or something nasty like that? egr, like you said?

Does the car have a PAIR valve on it still? it could be malfunctioning, when it does it's like a super-egr, it puts exhaust right into your airbox, which (obviously) gets all over your mafs, and everything.

There is a problem in that it starts at 1k, it should go strait to 1300 rpm and then slow down. Now, my car does this when it's really cold, but I'm not sure if it's my thick oil making it sluggish, or an actual problem. It could easily be something else, but I'm not about to spend more time or money diagnosing this particular motor, as long as it runs.

Maybe there's a problem with a solenoid or something on the iacv, even if you cleaned it.

use the FSM and it's diagnostics.

[spydy61]

have you ever figured out what the problem was with your car? i have a 95 240 with the identical problem....right down to the horrible gas mileage. 10mpg!

any help would really be appreciated!!

thanks,
spydy