Engine questions

[Radashar]

So recently I was having issues with engine shuddering and declining gas mileage, leading up to me hearing and then seeing sparks shooting between sparkplugs/wires. Since I never picked up the "working on cars" hobby and skills other than basics, I took it to a mechanic and had them replaced which solved that issue and led to another of course.

Pretty much immediately after that, I began having the up and down idle issues just like in the "Racing up and down at idle" thread (not allowed to link yet).

After spending a fair amount of time trouble shooting, he concluded my mass air flow sensor is bad and not working. He unplugged the wire connecting to it, stating that should cause the engine to shudder and cut off, but mine just kept on chugging. Hoping that he is right and it won't make something else show up, I should get the part and have it put in next week.


Would this problem be the main cause of loss of gas mileage? My 88 v6 is now getting about 160 miles to 11.1 gallons, which is probably half what I should get.

[RobertISaar]

all of the 88 MAF cars should have had the speed-density recall conversion done quite some time ago.... the MAF is actually only a IAT now.

[Radashar]

I'll have to see if we had that done. As far as I know it never had recall work done, but that could have been when I was younger and didn't know about things like that.

I'm mostly not convinced that the MAF sensor is the only problem. I swear I can smell fuel if I have windows down, but I could just be going nuts and smelling exhaust from other cars too.

[Money pit Beretta]

How old is the O2?

Check for vacuum leaks.

[Rettax3]

A worn-out O2 sensor won't likely cause it to run that badly... Look around under the hood, there should be a sticker under there somewhere if the recall update was completed. If not, ouch. I don't know if the dealerships will even do that work anymore. Have a full tune-up done to it -new plugs, PCV, and air-filter to go with your new plug wires, and as mentioned a new O2 sensor may not be a bad idea. That would be a good place to start with it. As Moneypit suggested, look for vacuum-leaks, and check all three ignition-coils to be sure they are actually delivering spark to the cylinders -unlikely but they may have been damaged when you were short-circuiting with the old plug-wires, or when the garage changed the wires. If everything checks out there, you may have to start investigating the fuel system (low fuel pressure, fuel leaking into the intake from a bad regulator, a faulty injector or injector circuit) and the MAP sensor. Good luck, you might have quite a journey ahead of you...

[Radashar]

The mechanic who replaced my spark plugs/wires obviously didn't know how to fix the issues that came up after the new wires were added to 25 year old other things and would have likely just eaten my time and gas money throwing stuff at it. It was nice that he was being so helpful, but I decided to screw it and go to Chevy. Eating dealer rates is gonna be less long-run than 40$ every 150 miles.

So I took it to the Chevy dealer nearby to get a full look and hopefully a fix. Found out that the computer is apparently too old for them to even read it with the diag-tools they have. They found one that can actually read cars from 88 and had it shipped over, so I'll take it by again tomorrow to get a real diagnostic done. They said that they already saw a couple things just by looking, but didn't want to make decisions just based on that. No charge and free ride to work while they looked at it for today. ($$$$$$$$$$ tomorrow right? )

Not looking forward to what its gonna cost, but its still likely gonna be less than a new car considering its only got 85,500 on it and is in great shape aside from all these lovely rubber and plastic pieces that are turning to dust.

[3X00-Modified]

There is a procedure to display any diagnostic codes through a sequence of blinking the ses light on the old ECU's... They should have known this. Granted that won't get you raw sensor data but it will show you what codes are present if there are any.

[Radashar]

It looks like the whole thing really is boiling down to a lack of maintenance during the life of the car before I took control of it. As Rettax said, I've got some work ahead, but once I get everything cleaned up and replace a lot of the 25 year old plastics and rubbers I should have better performance. The more complicated things I'll have to have done by someone, but little by little I'll see about replacing some tubing, etc myself.

The idling up and down has not gone away, but is happening much less now, and the only time it has stalled out is after shifting into park. I know that there was old gas that went bad in the tank and lines in the past, and that it was never cleaned out properly so that is another thing in the list as likely affecting my mileage. The fuel filter is new, but I suspect there is residue everywhere in my system.

[Rettax3]

These era cars also have an issue with what is termed an 'idle re-learn'. Every time your car loses battery power (even for a very short time, and even if the battery just gets really low -to the point that it will barely start or will not start without a jump), the computer 'forgets' where to set the IAC for a correct idle. There are a couple of ways to do it, and someone here can point you to one of the step-by-step procedures posted here more quickly than I can. Or, you can suffer through it until your car figures it out on its' own, which it will (sort of) eventually do. That could be a part of at least your idling issue...

[Radashar]

Yea, I saw the steps to do that on here somewhere. I need to go ahead and just do that. Although, I probably need to replace the battery first. It's fairly old and did die out once needing a good jump, and the Chevy guys said they see some low voltage in my electrical system.

[Rettax3]

You know, my Yellow Indy has been acting a little strange lately, and I got thinking about it -I think my battery is getting weak enough that the ECM may be 'forgetting' its' idle set-point while cranking... Hmm. Yeah, start with a fresh battery and go from there.

[Radashar]

So I got a new battery to put in, and figured I'd ask the guys at Walmart what this part was,

(I had been told "some random vacuum thing" by mechanic, who knocked it loose when replacing sparkplug wires and used the ziptie to hold it on, and chevy also) and get told it is a thermometer part basically. I'm guessing it has something to do with the IAT (or is?). So whatever it actually is, any thoughts on where to find one? Mine is pretty obviously shot from age.

[Rettax3]

'Random vacuum thing' is fairly close -that is the line from the EVAP canister. Basically, it flows gases into the engine that build-up inside the fuel-tank when the EVAP solenoid says 'go'. Low pressure, not very essential either. Gotta love those Wally-World-Wrenchers, boy howdy they are on top of it! Just find a rubber connector of the correct size -about 1/4" on one side, maybe 5/16" or 3/8" on the other? It isn't really a specific 'part'...

[ronaconda]

My vacuum line to my EVAP canister recently popped off mine and will give you the gas smell you were talking about.