sr20det HELP!

[SR_240]

i have a 1990 240sx se with a sr20det engine and it has a rough idle like when it drops below 1000 rpm it shakes pretty hard i was wondering if anyone knew anything about that?

[180fan]

Got a better description of the drop below 1000 rpm? Do the rpms oscillate, is it just on the rough side? Is the car warm and still idling rough? Does it come off the fast idle or has the fast idle phase already passed and gone into normal idle?

Oscillation usually suggests a vac leak. You can read my post on NICO's Online Nissan Mechanic section about my hunt for my vac leak.

Roughness could be your ignition system, timing, fuel delivery.

Ignition - check over your spark plugs. Let us know how they look. There'll be more advice depending on what the plug read tells.

Timing - warm up the car all the way. once warm, shut down the car, disconnect the tps, put an inductive timing light at the diagnostic loop at the back of the ignition harness and start up the car. Set your idle to 800 + or - 50 rpm and check over your timing. You should be at 15 BTDC, or second to last mark on the right hand side of the pulley when you're looking at the crank pulley. When you're at 15BTDC + - 2 degrees, tighten down the cas shut down the car and reconnect the tps.

fuel delivery - it's probably not your injectors if you're still able to idle under 1k. I would though check for clogging of the injectors and replace the fuel filter. Check your FPR though, you could be running rich or lean. Disconnect the vac line to the FPR and cap that vac line at your throttle. Did your rpms go up? If so, then you're fine. No, you've got a shot FPR. Did you check over your fuel pump? Did you replace it? I'd recommend getting a walbro or better if you plan on running more boost later. Also try wiggling your MAFS wire at the plug to the MAFS. If wiggling changes your idle, turn off the car, disconnect the MAFS wiring and clean the contacts.

There's probably some other stuff too, but I'm a bit buzzed to think of them now.

[grift]

also does your car do this when it is hot after you have been on the gas for awhile and is your BOV vented to the atmosphere? 180fan pretty much covered it

[SR_240]

alright thnx guys im gonna go have someone look at it but its only rough when it drops to about 500 rpm's and if its cold it will die but if it is warm its just rough

[180fan]

try hosing your iacv with carb cleaner. It's the small hose that connects to your cold pipe just before the throttle.

[Ripper]

it's the compression. i had this problem with my accord too. but it's really a problem for me, just more driving feeling. if you wanna fix it raise the compression (which i dunno how to do) i'm thinking adjust cam gears?

[SR_240]

my compression is 150 all the way across

[180fan]

only when cold then it's probably your coolant temp sensor or your iacv. unplug your coolant temp sensor and run the car. with the temp sensor off run your car. if it behaves the same, it's the temp sensor. If not clean your iacv with carb cleaner and adjust your idle so you don't idle at 500rpm. Your idle should be floating around 800rpm + - 50 rpm.

[SR_240]

it doesnt only do it when its cold its just that it will die when its cold but when its warm it still drops to about 500 and shakes but wont die

[S13/R32]

it just need a good tune, check timing it could be any thing from air flow senor to ECU setting like if u added new cams lots of things with the basic discription u gave
heres some basics to check- F.A.C.T.S.
-Fuel - injectors doing there job properly
-Air - obsructsions, airflow sensor?
-Compresion (150 no probs there)
-Timing - is it set correctly
-Spark - what ya spark plugs like dirty, too hot, too cold?

its helped me before l8r

[180fan]

Originally posted by SR_240
it doesnt only do it when its cold its just that it will die when its cold but when its warm it still drops to about 500 and shakes but wont die

Hmm...do you have a vacuum gauge? If you do, get one. Run a tee off your FPR and check your vac. You should be running between 15 in/Hg to 21 in/Hg. If your system detects the warm up, your coolant temp sensor shouldn't be a factor.

Personally I think it's a vac leak somewhere.

[S13/R32]

Originally posted by 180fan
Hmm...do you have a vacuum gauge? If you do, get one. Run a tee off your FPR and check your vac. You should be running between 15 in/Hg to 21 in/Hg. If your system detects the warm up, your coolant temp sensor shouldn't be a factor.

Personally I think it's a vac leak somewhere.

I think your way off. for exmaple if you were to disconect the hose from your PCV valve to your intake manifold your engine wouldn't be idling at 500 rpm it would be idiling 1000 rpm and then reving to 2000 rpm and then going back down to 1000 rpm repetively and would be doing this until u apply some throttle and then will behave like normal. this is leaning off the Air/fuel ratio. his problem sounds like too much vacum or fuel related or more commonly timing. if it is vacum check the IDLE SPEED ADJUSTING SCREW this screw allows the by pass port to be open or closed the by pass port is on the throttle body alowing more air to go to the engine when the butterfly valve is closed (eg at idle) if this by pass port wased closed or too obstructed there wouldn't be enough air strangling the engine. there is also a flap bypass in the airflow sensor (for when the flap is closed) with a by pass screw as well but this usally isn't a common problem i would check your sensors before u think this is a problem with ur engine.

[S13/R32]

check the
-MAP sensor (Maniflod Absolute pressure sensor, vacum sensor)
-Auxilary air valve

[S13/R32]

Originally posted by Ripper
it's the compression. i had this problem with my accord too. but it's really a problem for me, just more driving feeling. if you wanna fix it raise the compression (which i dunno how to do) i'm thinking adjust cam gears?

new piston rings or u need a head job (vavle seal regrind) put a squirt of oil in the combustion camber if the compression goes up from a standard compersion test its the piston rings (because the oil seals the gap between the piston rings and the clyender wall) if it doen't it ur valve seals

sry for going of topic

[180fan]

Originally posted by S13/R32
check the
-MAP sensor (Maniflod Absolute pressure sensor, vacum sensor)
-Auxilary air valve

#1 no map sensor on the sr. anyone with any previous experience with nissans knows that they don't use MAP sensors, they use MAFS.
#2. AAV is a part of the IACV for the SR.

Also when your car is warm, the ecu will go off the fast idle aka if the motor's running rough, you'll be less likely to feel it at high rpm vs. low rpm.

Next, if you remove the PCV from the system, you don't get oscillations in your rpm from 1k to 2k. All the PCV does is vent the extra pressure from the crankcase back to the intake. Check that, it's a one way valve and will not cause oscillations like you're describing unless you've got a vac leak. Check the FSM if you don't believe me.

If you could also check to make sure you've got all your vac lines that you aren't using are capped then that could also be a culprit.

If the IACV was closed or clogged, the idle will go to crap yes I do agree with you on that point but if it were, the idle would be rough all the way from the start of the motor. Hence my suggestion earlier about hosing it down with carb cleaner.

Assuming you've gone through the check list I listed before, chances are more than likely a vacuum leak since there aren't may components that contribute to the idle system. Coolant temp sensor, mafs, IACV, and the actual vacuum lines.