i had this problem for almost half yr, this is really flustrated me.
car: 86 gxl N/A manual stock, idle rough after engine warms up, but it drives totally fine.

i had cleaned BAV, adjust TPS, changed spark plugs, cleaned battery terminal, still idle rough.

And i recently found the vacuum leak at the throttle body, where he rod comes out, and this rod holds the top two throttle plates near the intake.

so i bought one throttle body off from ebay, chean it up and had mine replaced, and it still idles rough.

should i replace the fuel injector and its grommet as well? anyone had my issue and had it solved?

please help me out!

 

Sounds like you may still have a vacuum leak.

Check BAC valve operation per FSM; make sure it is connected.

Check AWS/water thermo sensor per FSM; check the resistance of WTS at known temps.

any engine ECU codes?

 

If it's "hunting" for idle, you have a vacuum leak or improperly routed vacuum hose as mentioned earlier. Take apart the intake manifolds and check all your hoses. Might be a good time to replace lines with silicone hoses.

You said you cleaned the BAC and adjusted TPS, but did you check they are testing out to be within specifications using an ohm meter? These are somethings to look at.....

 

i found that vacuum leak at the throttle body with my friend's smoke machine. not anywhere else sees the leak.

and i did set the tps to spec with a ohm meter.

all hoses clips are connected properly.

i am goni to play around with the thermowax and other components after work today.

 

Setting the TPS or a component, vs. testing if its within specifications are two different things... Take my and calpatriot's advice and go through each component....

Also, just because you don't see any disconnected vacuum lines doesn't mean that eliminates the possibility of a vacuum leak or improperly routed vacuum hose. Also, don't forget bad intake manifold gaskets will cause vacuum leaks.

 

i had tested the bav, it clicks once i applied electricity to it, so thats working.
before i change the throttle body, TPS was off from it's spec, so i correct it, but didnt solve the idle problem. TPS may go wrong?
after changing the throttle body, stilll rev rough, but i didnt do anything else after replacing the throttle.
i used a smoke pro to find the vacuum leak(before replacing the throttle), only saw one spot was leaking, where at the throttle body, which i explained the location on last thread. i searched at least half an hr for another leak, no sign, does that mean no vacuum leak elsewhere other than the throttle?
for engine ECU code, is it the code that lable on the ECU? why mess with the code, to ensure it is the right ECU for my car? but my was driven and idle fine for the last two yrs with the same ECU.
if i have time today after work, whats the first thing i should go for, replace the TPS with my old one? the one that i had set to spec? and the suction unit?
one thing i hate to own a single home is too much law work, so i have to squizze/manage after working hours, and i cant work in my garage since my other car is sitting there waiting for me to get it fixed. so really i have 2 hrs(before sun goes down).
one last thing, i had seen suggestion about using different grade of gas, go for premium of regular? i had used both, regular mostly.

 

The ecu codes he refers to are the codes which can be pulled up by using the twin led light setup. The TPS would definitely need to be set again for as I understand it it you put on a different throttle body. If the newer throttle body came with a TPS or you are using the TPS from your older throttle body it needs to be reset.

http://www.teamfc3s.org/info/article...odes/main.html

The clicking of the BAC may not tell you it is full proof. With the engine properly warmed up turn on the A/C and pull the plug off the BAC. The car should stutter hard if not die out altogether. You could also squeeze the vacuum hose of the BAC with a pair of needle nose pliers to see if the rpm changes at all (no A/C on).

 

i set the tps to spec, which is 1volt with warmed up engine, still didnt work out. the tps was very close to 1 volt anyway.
and i did squeeze the vacuum hose of the BAC while idling rough, the rpm drop down to around 1k stable, if i pull the vacuum hose off, the engine dies out, inorder to have 1 k stable rpm, i need to squeeze the hose close to bottom out.
is the BAC goes bad?

 

Don't know if you tried this, but you could jumper the initial set coupler, which will change the way the BAC can affect the idle. Jumper the coupler and start the car up and observe for any changes.

 

jumper the initial set coupler? which means? i dont get that.

 

i found this on a rx7 technical site, looks like this will solve my problem, if turning that capped screw will lower the "plumbing" output, my idle will be back to normal. i am goin to find that capped screw and hopefully it works for me.

*****Please be well aware that the base idle speed does not come from the BAC valve itself, but from some "plumbing" within the intake. The base idle speed (750 rpm) can be adjusted by turning the capped screw on top of the intake. It has nothing to do with the BAC valve, and this is why you should always adjust the base idle speed by setting the initial set coupler or disconnecting the BAC connector (at the BAC valve).*****

 

For N/A idle speed is controlled by screw on TB.

On Turbos, idle speed is controlled by BAC screw.

 

it is N/A, is it the screw that on top of TB, cover with a rubber cap? turn by a screw driver. i did adjustment on that, no changes on idle.

and i did adjust the hex screw on the BAV too, it locates at the center of the blue clipper, i can get the car idle at 1500 at stable, but there's "bababababa" sound from the engine(sounds like it come out from a exhaust area), and the engine shakes kinda bad.

 

The BAC on a n/a is "non adjustable."

 

yes, my friend told me that if there is nothing in side taht hole, then teh Byass Air Control Valve is non adjustable, that hole is right under the air inlet for the BACV.

i dono how much longer i have to stuck with this idle problem, i am thinking of doin a turbo swap once i got the money.

diregard the pipings. does the 13B tt engine swap from gen 3 goes into gen 2 without any modification on fitting?

 

Did you start the car with the initial set coupler jumpered as suggested?

 

If the screw on top of the TB is not doing anything at all, double check the black spacer and make sure you didn't put it on backwards, and that the holes are not clogged.
Mine was backwards when I purchased the car, and when I swapped my intake to s5, the new one I received was 100% clogged.

 

The hex screw on the N/A BAC is not for adjustment. There is a chance the BAC might have been thrown out of adjustment if you did force the hex screw to turn. If your engine is shaking, you have issues with something other than idle.

Are your fuel injectors clean? Time to start looking elsewhere for issues... Also, do look to make sure your adjustment screw hole on the TB is clean and free of carbon.