Help! 96 Corrolla bad idle

I need some help from those experienced on troubleshooting toyotas. Background: Mom's 96 Corrolla with the 1.8, auto, 260k miles of neglect. My mom last washed the car sometime in the last decade and maintenance has been the bare minimum I can do to keep it road worthy.

Sometime recently it started idling very poorly and occasionally shuts off at a light, especially if you have the air on. It wasn't a sudden change from what I can gather but has been getting steadily worse for some time. As you pull away it hesitates a little but once it's over 1000rpm it runs pretty good, has power, fuel economy hasn't tanked. It feels like it's got a dead miss at idle - engine shakes, exhaust kind of 'puffs' at the tip. In park it's not horrible, but in drive or reverse with foot on brake, it's really bad. IT seems to get a little worse as it warms up. Engine was throwing one code due to the O2 sensor being unplugged. It had been that way a while according to Mom. Cleared the codes and it hasn't triggered a CEL since

So here's what I've done so far that hasn't cured it: plugged in O2, new plugs ( they were ashy and the gap was way over, worn out) new cap & rotor.

One possibility I thought of was a bad plug wire. I checked the resistance in the spark plug wires and it's in the right ballpark. I replaced the wires about 3 years back. You can unplug one wire at a time and the hear the idle change. If one wasn't firing I would expect to unplug it and see no change in the rough idle.

I slapped a vacuum gauge on it and it reads about 12-14 in and the gauge flutters about 1-2". If you bring the rpms up it stabilizes and loses the flutter. Under load with the ac on, that drops to 10.

I checked all over for a vacuum leak - visual inspection, auditory inspection, and by spraying starter fluid all over the place. Idle never changed. When I took the vacuum gauge off the idle jumped up while the manifold vacuum line was uncapped. Both of these seem to rule out a manifold vacuum leak

I'm a little concerned it might have jumped time, but I just did the timing belt less than 10k ago, and the tension seems about right. I tried to check the timing with my old timing light, but it won't trigger when hooked to the ignition wire. Is there and easy way to verify the timing?

So...I'm stumped. I hate to buy wires and put on it since they tested okay ( assuming I did it right) but is that the next step? Anyone have any experience with these little Rolla's? Is there a common failure point I should know about that causes this?

Wait, sorry, the engine is a 1.6 the 82 Rolla I had was the 1.8.

Vacuum is really low. Should read 17-22. Late ignition or valve timing, low compression, intake leak somewhere.

^ I'm with him, that's low. When you open and close the throttle quickly what do the readings look like?

You might have more than one problem.

Does it have the intake manifold that looks like an exhaust header? They crack sometimes.

yes, vacuum's definitely low. Compression crossed my mind as the car does smoke a little sometimes, but I don't have a compression tester. Need to borrow one...

On a quick crack of the throttle the vacuum drops and then recovers to wherever it was, I think. DIdn't do that as a specific test but did blip the throttle a few times and I think that was the reaction.

It looks like a small aluminum loaf pan that is connected to the head with tubes that might resemble a header.....? Any good way to test for a crack?

Looks like this, but E36 M3tier:

Sounds to me like plug wires.

If the insulating properties of long boot that goes through the valve cover start to break down it will arc over to the valve cover rather than firing the plug with a strong spark causing most of the symptoms you describe.

As a short term test try wrapping the boots that go through the valve cover with electrical tape to see if the insulation changes/improves things before springing for new wires.

Looks like a 4AFE. If you grab the plug wires while it's running, do you get thrown across the shop? If not, I'd say they were probably OK.

There should be an idle air control valve. I suppose that could go out, but I'd continue to look for a vacuum leak first. Power steering? Be sure to check the vacuum lines going to the rack.

You could always put a 20 valve in it....

small valve on the side of the intake... has vacuum in and out and a 2 wire plug. In your photo it is on left edge of manifold. Check to see that this is operational... this is the idle up bypass for loads, and cold idle

Its a Toyota, you have to clean the IAC a lot to keep it idling right, though the vacuum reading make me think its more than that. When is the last time it had a timing belt? Maybe it jumped time. 4AFE isnt a valve muncher.

Dumb thought... Intake boot from the filter to TB. All of the symptoms you describe (even including the low vacuum) could be because there is most likely a huge tear in the bottom of that bellows.

Once you determine that I am right, donations for my awesomeness can be mailed to me. :)

what do I win?

t looks like a small aluminum loaf pan that is connected to the head with tubes that might resemble a header.....? Any good way to test for a crack?

The picture you posted does not look like the thing i am talking about. Cast aluminum intakes almost NEVER crack. The only ways i would suggest to check for leaks is the stuff you already did. However, it doesnt hurt to retest if you start to doubt the job you did the first time. A lot of times i will take a water hose on full blast and just drown the intake looking for an RPM change, and if it DOES change then i will try to narrow it down with a more precise method which may still involve spraying liquids at it.

It sounds like you've taken all the right steps so far, but also do what Curtis said, and check to see if there are are any hidden rubber or plastic fittings that are cracked. Dr Hess mentioned a vac line to the PS rack, I've never heard of one of those, but thats the kind of hidden thing that I'm talking about. I would also double check the cam/crank timing. I've never seen a belt jump time, but stranger this have happened.

Next you should do a compression test. Do it first on a completely cold engine, then warm it up and try again.

I recently had an engine that had a failing head gasket between cyls 2&3, it also had low vacuum and ran like crap until it completely warmed up. The compression test on the stone cold engine is what gave it away.

If it passes the compression test, or is low but has even pressure across all 4 cyls, I would try the seafoam treatment.

. .

Jumping timing was something that I'm concerned about, but I just did the timing belt less than 10k miles ago, so I know the belt itself is in good shape. The tensioner seemed good at the time, and the belt tension seems okay after pulling the top cover and poking around.

Is there any way to check the timing with a standard timing light? I hooked mine up but wasn't getting anything while connected to the #1 plug wire. The bulb may be bad in the TL, but I'm not sure. Should an inductance trigger light work on these plug wires? If I can't use the light, what's the best way to check it?

Curtis, I'd like to think I would have noticed a big split in the intake hose, but I'll check it again on the off chance that you are as awesome as you say you are, because that would be awesomely easy to fix.

The idle up bypass valve bears investigation, as does the vacuum conx at the steering rack. One of the other things I did to it was replace a power steering hose that had been leaking for some time, long enough to take out the rear engine mount (the mount requires dropping the front crossmember and control arms by the way, yuck.) It's entirely possible that the fluid softened the vacuum line and caused a leak. I didn't really see the vacuum lines, but I wasn't looking for them either.

Those checks and a compression test will be my next stop.

A regular inductive pickup timing light will work fine with that system.

Sooooo.....I finally got around to checking the compression on the Corolla. I'm afraid it's bad news, but I need you guys to help me figure out what kind of bad news.

Cold Check:
1- 150psi
2-105 psi
3- 50 psi
4- 170 psi

Hot check:
1- 155 psi
2- 120 psi
3- 50psi
4- 170 psi

So...I would think if the head gasket was gone between 2&3 they would read the same. Maybe. Maybe not.

Cam lobes gone / going? valves? I haven't had time to pull the valve cover and eyeball them.

In any case, I think I'm sending it to a pro, but I'd like to have a direction to point them. I have very little free time right now time, and I've never wrenched inside a motor. I don't want my first time to be in fits and starts when I'm already tired from working all day. I want it to be with candles, and roses....oh sorry, Different topic.

A new 7AFE is like, what? $20?

Could be a head gasket, and they wouldn't necessarily read the same. Or a hole in the piston, or valves, or .... Either way, it's coming apart. I think I would pull the head an inspect it, then decide on gasket versus new used motor.

See if the offending cylinder's exhaust valve has any lash left in it.

Dr. Hess wrote: A new 7AFE is like, what? $20? Could be a head gasket, and they wouldn't necessarily read the same. Or a hole in the piston, or valves, or .... Either way, it's coming apart. I think I would pull the head an inspect it, then decide on gasket versus new used motor.

^^ This. You don't know just how bad it is until you pull it apart.

Kenny_McCormic wrote: See if the offending cylinder's exhaust valve has any lash left in it.

Agree, Check the valves first. Had this happen with a friends Focus when he put new cams in and got the wrong shim in one cylinder. Exhaust valve never closed so no compression.

260k miles. That is about the time that the rings let go. Seen that on a few 4ag engines. The compression test seems to confirm that as a possibility.

New rings and it should go another 200k miles.