93 Sc400 Idle Problem

[soarer400]

hi everyone,

What could cause a 1 owner SC400 with a little over 100k miles, to run rough?

I already done the folowing.

Cleaned idle control valve,

replaced air flow sensor,

Cleaned the trottle body,

checked spark plugs & they look good.

Doesnt seem to be a missfire.

Car idles at low RPMs with uneaven exhausts.

[Tomj8]

hi everyone,

What could cause a 1 owner SC400 with a little over 100k miles, to run rough?

I already done the folowing.

Cleaned idle control valve,

replaced air flow sensor,

Cleaned the trottle body,

checked spark plugs & they look good.

Doesnt seem to be a missfire.

Car idles at low RPMs with uneaven exhausts.

Just some places to start - I assume you checked for dirty air filter and found it OK. A vacuum leak can cause uneven idle too. Have you run a compression check just to verify the valves are OK?

[1992LexusSC400]

Always try the simple things first... Check for all vaccuum leaks first, then I would run a can of Seafoam through it. It wont hurt it, but it may help the rough or low idle a bit. I had the same problem and I adjusted the linkage on top of the throttle body or just simple tightenend it up to pull the idle up. Now its perfect.. Sitting dead on 600 rpm at idle in drive and 850 in park.. A little high in park but its smooth after the motor and trans mount replacement.

[soarer400]

Ok, the low RPMs were caused by a non working air flow sensor. (was code 31 airflow meter.)

Now with another used working AF sensor, I get bucking 1k - 2k RPMs.

already injected 1/3 pint of seafoam into valves, through air vac hose.

Now i dont get any CEL.

wonder what could be causing it.

? approximately $$$ for such to be fixed at a shop?

[soarer400]

Ok, the low RPMs were caused by a non working air flow sensor. (was code 31 airflow meter.)

Now with another used working AF sensor, I get bucking 1k - 2k RPMs.

already injected 1/3 pint of seafoam into valves, through air vac hose.

Now i dont get any CEL.

wonder what could be causing it.

? approximately $$$ for such to be fixed at a shop?

Problem Fixed! If anyone has a similar problem, you might want to check and clean the entire IDLE Air control Valve with some oil.

Thanks

[eatingupblacktop]

Ok, the low RPMs were caused by a non working air flow sensor. (was code 31 airflow meter.)

Now with another used working AF sensor, I get bucking 1k - 2k RPMs.

already injected 1/3 pint of seafoam into valves, through air vac hose.

Now i dont get any CEL.

wonder what could be causing it.

? approximately $$ for such to be fixed at a shop?

Problem Fixed! If anyone has a similar problem, you might want to check and clean the entire IDLE Air control Valve with some oil.

Thanks

Just curious, you mentioned cleaning the iacv in your first post. What made you do it a second time?

[eatingupblacktop]

Ok, the low RPMs were caused by a non working air flow sensor. (was code 31 airflow meter.)

Now with another used working AF sensor, I get bucking 1k - 2k RPMs.

already injected 1/3 pint of seafoam into valves, through air vac hose.

Now i dont get any CEL.

wonder what could be causing it.

? approximately $$ for such to be fixed at a shop?

Problem Fixed! If anyone has a similar problem, you might want to check and clean the entire IDLE Air control Valve with some oil.

Thanks

Good of you to post your solution. Just curious though, you mentioned cleaning the iacv in your first post. What made you do it a second time?

[soarer400]

Yes, first i spray-cleaned the valve with a carb cleaner which didnt change anything at all. Later, second time I basicaly had to take it apart and smooth its mechanisms with oil. Then i tested it with direct battery voltage, and??? It works! Put back in, start car, excelent RPMs. Very simple. Thanks.

[dawhorl]

Ok, the low RPMs were caused by a non working air flow sensor. (was code 31 airflow meter.)

Now with another used working AF sensor, I get bucking 1k - 2k RPMs.

already injected 1/3 pint of seafoam into valves, through air vac hose.

Now i dont get any CEL.

wonder what could be causing it.

? approximately $$$ for such to be fixed at a shop?

Problem Fixed! If anyone has a similar problem, you might want to check and clean the entire IDLE Air control Valve with some oil.

Thanks

did the idle air control sensor cause you to also have power loss?

[tan92sc400]

im having the same problem with my 92 sc 400, rough idle, die out sometimes, was wondering if its the IAC if that would cause a random jolt sometimes, almost like the transmission, but i hear the transmissions are beast. Happened once at 120 and once around 50, wasnt getting on it either times, i was cruising around 120. Any ideas?

[Servidor]

Where is the IAVC on a SC 400? Mine is a 93

[machthree805]

Could you tell me exactly how you cleaned your idle control valve? Where is it located, what tools will I need? My car is doing the same thing and the repair shop says the valve alone costs $800.

[gaston1118]

hi my name is gaston new comer to the form this is my first sc400 my bro had one when i was 13 and i feel in love with them so i bought one when i sold my starion... my sc400 is a 1993 needs some loving but i wont to get it runnung good beffor i get the seats redone.. plz can you help mee?

yeah my cars doing the same thing i have cleaned the IAVC twice but i used wd40? do you thinke i messed it up with that? i got a new mass air flow too. ever sice i cleand the iavc and put it back and pluge the new mass in the car will struggel to get from from 800 to 2000 rpms when in drive. idk if i should get a new iavc and see if that will fix it?? can you plz help me with thiss??? car drives amazing with the mass unpluged...

[1JZPWRD]

i would clean the iacv with some carb or brake cleaner and would replace the two bearings also. very simple to do. search www.lexls.com then click on tuitorials under maintenance. good luck

[monroepops]

Hey Gaston 1118, my name is Alton. I'm new to the forum also, I also am having the same problem with my Lexus SC400. Never saw nor heard of Sc400's until I purchased my 92,great vehicle.worth restoring. Wish you the best with your baby

[SeanGrac]

Check the throttle position sensor (TPS)