Repair Plans: Advice requested

[deejay1272]

First off, let me say that this forum is spectacular. Big thanks to the developers for making this possible for all of us aspiring gear heads. I’d be lost without this site!

On to the rub: I'm planning on performing a few repairs and tune-up operations this weekend so I thought I'd post to get some feedback from the experts beforehand. There's kind of a lot to cover here, so I'll try my best to keep this post as organized as possible.

The Problems:
1) The Terc is very difficult to start
2) The idle oscillates wildly after I do start the car and it only idles appropriately when it’s running very warm – and even then, it’s not the smoothest idle I’ve ever felt, so there’s some room for improvement I think.

My Theory: That the choke flap is being held in the open position, therefore improperly leaning out the fuel mixture. I imagine that a vacuum leak is responsible for the idle situation. I have confirmed that the choke flap doesn’t close properly when the engine is cold and it appears as though part of the throttle lever (could be the TP lever?) is obstructing the full range of movement of the shaft that dictates the choke flap position.

My Proposed Plan of Action:
1) Thoroughly read the FSM!
2) Service the choke system by trying to get that throttle lever out of the way. This is where I need some advice. First off, has anyone ever seen this? Any tips on how to proceed? My plan is to simply disassemble and start cleaning away. The FSM has some detail about how to “service the choke system,” but it doesn’t include a whole lot of useful information.
3) Inspect the PCV system and valve. I’ve heard that this can be the source of many poor idling issues.
4) Run through the vacuum lines and hit all connections with a squirt of carb cleaner. Word on the street is that this is a slick way to quickly spot a vacuum leak.
5) Inspect the timing by utilizing a strobe timing light. Again, I need some advice on how to do this since I’ve never done this before. What exactly am I looking for when the strobe light kicks on? I plan to do some reading about it, but advice about how best to proceed would be helpful.
6) Possibly replace distributor cap and rotor if necessary.

[4wdchico]

Sorry but: don't bother with any of the above. is your compression good? If so, I strongly suggest that you fully functionally check every part of the vac system. As in every hose the TVSV and every diaphragm. It will take you at least a day of scratching your head and reading the FSM. Possibly more. Just go system by system thru the emission control system section. Check for vac leaks with pure undiluted propane, not carb cleaner spray. Make sure the four carb retaining nuts are snug and that there are no vac leaks at the carb base plate, carb throttle shaft or anywhere in the intake manifold system. Disconnect and cap off the vac brake booster tap at the #3 intake runner to eliminate any possible leakage thru the brake booster system. Check that point where the brake booster tap screws into the #3 intake runner for tightness & leaks.
Make sure that the AAP diaphragm is not leaking fuel into the vac system. Make sure that the carb fuel level is correct.

Get a decent vac gauge and educate yourself fully in using it. The vac gauge is the most under appreciated diagnostic tool there is.

Early '90's 4 cyl. camrys are plentiful in the junk yards these days and have some long 'yota specific vac lines between the intake manifold and distributor. Go get a few of these nice long chunks before you start your project. You will be happy that you did.

If you do the above, not only will you have a much better grasp on how your car works, but you are much less likely to miss something and have it come back later & and bite you in the ass.

[Petros]

I would first check all the vac lines and systems as 4wdChico suggest (I personally like the carb cleaner way of finding vac leak, I have also used propane method but found it not as exacting). Also there is an idle adjustment for both cold (when the choke is closed) and for warm when the choke is open, it is next to where the throttle cable attaches to bellcrank on the throttle shaft. If you have no vac leak, you need to adjust the speed at the throttle plate.

The chokes system is usually reliable, a quick check is to take the cleaner off when it is cold, it should be open (from when last running warm), and than move the throttle to full open postilion and release, it should slam shut. To double check start the engine and see if it opens up when warm. If it works, that is not likely the problem and no further testing is required.

I do not think spark timing would cause that behavior either, it is a good idea to check the timing, but it will not change the issues you asked about. It is a simple tool to use, you put the signal clip on the #1 spark plug wire, and point it at the front pully when it is idling (dist. vac lines off and plugged) and see were the mark on the pulley appears on the front cover indicator. It should flash in time so it appears the mark is in one place (it helps to clean the mark and pointer, put white-out or similar in the timing mark on the pulley). You adjust the timing by slackening the bolt holding the base of the distributor and rotate the distributor slightly (than re tighten the bolt). You have to get it to idle down to the correct RPM first, or you will not get the correct timing because the spark advances with higher RPMs. So you have to get it to idle down first.

Not likely the PVC or wires cap and rotor will cause idling issues, if they need replacing than do it, but it is a waste of time if you think these issues will solve these idle symptoms.

Good luck.

[deejay1272]

is your compression good?

Yup - Just tested this 2 days ago. I'm running at 180-190 PSI in each cylinder. I have a 3A SCV engine so I imagine that this is a bit higher compression than you're used to if you have the 3A or 3AC in your Tercel.

Thanks for the advice. I'll post later on this weekend when I know (or don't know) more.

[Snax]

This probably doesn't help too much, and probably qualifies as the 'just throw money at it' approach, but when mine was running rich, I took one look at that carburetor and vacuum system and decided a Weber replacement was in order. The idle control isn't perfect with the Weber either, but at least I don't have to study the manual to work on it now.