lights make rpms jump? ?

Hey guys, new guy here. I have a inquiring about my lil 89 sr5. It has the 4af carb and for some magical reason when i turn on my headlights the rpms shoot up to 3grand and stay there. Turn them off and down they go to 800. Bit of history on it. I bought it about a minth ago from a chick cause it didnt run ( been sitting too long no gas in the lines, now runs great. Just did tune up on it, plugs wire cap rotor fuel filter ect.) now it runs great motor sounds and revs anyway i was thinking amp draw from the alternator but that normally lowers rpms on fi ( where most of my exp. Is) also if anyone knows where or what i should search for cause parked driving or w/e if i rev it and get off the rpms hold for about 2 seconds then slowly drop. It can be from a small blimp to full rev they hold and then drop rather then normal dropping. In an fi this would be tps or idle speed but in carb



any advising or guiding would be great thanks all...

Tnation has been a great help thus far....

Reply 1 : lights make rpms jump? ?

The carb has a dual diaphragm vac operated throttle positioner. It's mounted on side of carb.When there is a load on engine it raises idle speed. It also holds throttle open slightly when decelerating . It has two adjustment screws and cams. Have someone help you and watch it while they turn on the lights. You will see the cam move and know which screw to adjust. Also check for any vac line leaks on the throttle positioner. Look at Fig 2 in link for pic of throttle positioner.



http://toyotadiesel.com/photopost/da...l_overhaul.pdf

Reply 2 : lights make rpms jump? ?

Great, thanks. makes since, i'll take a look at it tomorrow after work with my brother and keep ya posted. hopefully i can get it dropping a bit more normally. out of curiosity, can those be eliminated with out replacing the carb to say a weber? cause god its got vac lines

Reply 3 : lights make rpms jump? ?

I remember all the vac lines when I had my 87 4A. I wouldn't attempt to eliminate any of them or the components. It all works together and if you start disconnecting you will have other driveability issues. I have a hunch your present problems stems more from a vac line leak and not necessarily an adjustment. Should be easy to find. When your helper turns on lights listen for a vac leak in addition to watching the throttle positioner. If no leaks found then try adjusting the adjusting screw counter clockwise on the cam that engages on throttle positioner with the lights turned on.

Reply 4 : lights make rpms jump? ?

well great news , found the screw and the cam. no leaks on the 20 miles of vac lines there so all good :-D . adjusted the screw and was able to get the rpms down to normal with the lights on and also rectified the revving issue. thanks the lil corolla is now running like normal. a bit smookie but probably cause i seafoamed the gas tank with almost no gas in the tank ( light has been on the whole time i been messin with it ) hopefully when i go fill her up that stops and i can pass my smog test.

Reply 5 : lights make rpms jump? ?

Good job on the adjustment. If you want to check it for trouble codes prior to it's breath test here is a link. On the older OBD 1 systems stored codes don't always trigger the check engine light. Might want to replace air filter and oil change prior to test and take it out on the highway to get cat converter good and warm and keep it running while waiting in line.



http://www.troublecodes.net/Toyota/

Reply 6 : lights make rpms jump? ?

thanks, didnt think this was a obd1, obd0 maybe. the air filter i changed since it looked like it backfired at one point and burned it before i bought it . did the oil change and now im considering getting a new thermostat since i have read that alot of these carb'd corollas have trouble passing if the engine and cat arent warmed up right.

Reply 7 : lights make rpms jump? ?

Good idea to change thermostat and flush out cooling system while you are at it. When you replace stat be sure to park on incline. Remove cap, turn heat on high, and run till warmed up to burp air (alot of air pockets in system) and top off fluid. Prior to your test check that all the vac lines are hooked up to EGR and vac modulator and that it operates. If it isn't working it would spike your levels and flunk it. Sometimes older toys end up needing a new cat to help them pass the more stringent regulations in your area. Remember reading from another poster (california) that they have some program that if remember right subsidizes the payment for parts such as for a new cat in order for car to pass.

Reply 8 : lights make rpms jump? ?

Thanks. The cat seems to be new(er) since it looks not as worn or timed as the rest of the piping. Now running the risk of sounding a total noob what is a vacuum modulator? I miss my old gts.... So much simpler for me with efi..... ::-D:

Reply 9 : lights make rpms jump? ?

Does the engine RPM actually increase, or is it just the tachometer that goes up?

Reply 10 : lights make rpms jump? ?

the engine was revving up. but we got it figured out, thankfully it wasnt just the tach that would have royally boned me. lmao.



p.s. loved the autox thread, stumbled apon it about 2 months ago hoping to get this sr5 running like eage8's

Reply 11 : lights make rpms jump? ?

This link shows pic of vac modulator and its proximity to the EGR plumbing. The information in article may not apply to your particular engine. More for general reference.



http://www.autoshop101.com/forms/h61.pdf

Reply 12 : lights make rpms jump? ?

10-4, turns out i knew what it was just didnt know the name, thanks again.

Reply 13 : lights make rpms jump? ?

Quote:

Originally Posted by sincity.rolla the engine was revving up. but we got it figured out, thankfully it wasnt just the tach that would have royally boned me. lmao. p.s. loved the autox thread, stumbled apon it about 2 months ago hoping to get this sr5 running like eage8's

Thanks.



You'll get it running right.

Reply 14 : lights make rpms jump? ?

Thanks... But tell that to the wife who thinks i sold my 97 jetta for a p.o.s. ( little did she know that is worse and was on the verge ogre dying., rod knoc, and the trans was shot) glad to be back in a Japan built machine.