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88 Gts Stalling When Coming To A Stop



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Greetings...new member here. I am original owner of an 88 GTS 4AGE 5 speed, fresh rebuild (but this problem was happening before the rebuild). It stalls (or at least the idle drops so low it wants to stall) after slowing down...usually after warmed up and driving on the freeway. After reading up, I feel it's the EGR or the IAC (both original) though please educate me as there are also the VSV and MAP sensor that could be problems too.

Fix #1: I checked and adjusted TPS...no change. Also, fuel injectors and fuel filter are good.

Fix #2: I removed the throttle body to clean the IAC but the 4 screws holding it on are frozen and I cannot remove it so I just sprayed it as best I could. No change.

Fix #3: I used a vacuum pump on the EGR, and the diaphragm slowly loses half its vacuum over about a minute...does this mean it's bad?. My manual states that the vacuum should be low at 3500 rpm and zero at 5000 rpm and it isn't...it has some vacuum at 3500 but does not change to 0 at 5000 rpm. As an experiment I temporarily disconnected the EGR (plugged the vacuum line going to it) and did some freeway driving to see if the problem would stop, but it hasn't. Does this "check" eliminate the EGR as being the culprit?

Thanks in advance for a long question.

To be sure I understand the issue - the stalling is only at idle speeds? At highway speeds, or when the throttle is wide open - there is no problems?

The EGR should hold vacuum, from what you described, sounds like it has a small hole or crack in it. So the EGR is a possible suspect. MAP sensor - no easy way to test them, either they work or not. They can be tested with a scope or high impedance DMM. I generally don't recommend you use plain volt ohm meter - as their impedance may not be high enough, also with the wrong setting, you can short out the electronics inside the MAP sensor (not sure on this Toyota, but this is the case on other makes).

Could be a vacuum leak - those are pretty common after a fresh rebuild - as the engine is usually much tighter (produces stronger vacuum at idle) and can cause the existing hoses and connectors that were marginal but still OK with the old engine, start leaking now or get worse with the fresh engine.

Can also be an ignition issue - either weak spark or the timing is too retarded, causing the low idle. Quick test is to put a timing light on it and verify that the timing is good.

Can try an old school trick - take a spray bottle and fill it with some water with a little detergent or dish soap in it to act as a surfactant. Hit the vacuum hoses, around the throttlebody, intake manifold, EGR tubing, etc. while the engine is idling. If the idle suddenly improves or changes - you found the vacuum leak.

Great, thanks for your advice.

It stalls only when slowing down to a stop, for instance when hitting traffic from 65 mph or coming to a stop on an offramp. And then only some of the time...it is not predictable. Sometimes after a stretch of highway and then hit city traffic, rpm's will drop to 500 or so and be rough idling in traffic. Shifting to neutral does not change it. Blipping the throttle can bring up the idle to normal sometimes. Throttle wide open there is no problem.

I was hoping that by disconnecting the EGR that would give me the answer, but the problem was still happening so I don't think the EGR valve itself is the suspect. I have not found any vacuum leaks and this was happening before the rebuild too. The timing is good.

Could this be the IAC? It seems those also cause stalling issues and unfortunately I'll need to take mine to a machine shop to have them remove the 4 phillips screws (3 of them are frozen and half stripped at this point).

Yeah, that sounds exactly like a textbook case of a clogged or stuck EGR. Seeing no change when disconnecting the EGR points to a stuck valve - as it is usually closed with no vacuum, opens with vacuum. I'm betting that the assembly that runs from the exhaust manifold to the EGR's pressure chamber (where the EGR valve's "plunger" sits on) is completely full of carbon. Had a similar happen to my 1996 Camry - was a nightmare to try and take out because of clearance issues - but once I got it out - that tube was completely chocked closed. Also sounds like the diaphragm might have a crack or leak in it - so the EGR vacuum modulator could also be suspect.

It is possible that the IAC is faulty as well, but that usually manifests idle issues from a cold or warm start and usually ends up with an excessively "fast" idle. I could see a case where it could cause the idle to drop too low, but most of the time, issues with the IAC causes the idle to be too fast.

I'd try soaking the screws with some good penetrating solvent - PB Blaster, Liquid Wrench, or Kroil/Aerokroil. Slot the tops, and use a regular slotted screwdriver to try and back them out. I've gotten out some pretty badly corrosion welded bolts with that methods - just take more time, to allow the penetrating solvent to wick into the threads. If they don't budge under that - then you can resort to a machine shop.

Thanks. Interesting about the egr valve. I had it off during the rebuild, including the assembly going to the exhaust manifold and cleaned them out really well (though did not spray anything on the EGR diaphragm itself...I read that could damage it so I just cleaned the pipes). No carbon left so I don't believe anything is blocked. The modulator which sits next to the egr valve appears good also. The bvsv also passes my manuals test procedure. I'll try your procedure for the IAC...good idea about cutting slots in the screws. It has 200k miles on it and never been cleaned so I'm hoping that is the culprit.