My 87 has a little vibration whether at idle or while driving. It also likes to hesitate for a sec if you give it a really quick rev. Does this sound like a coil that's going? Thanks.

 

No, its a fuel delivery problem or vacuum leak.

 

I agree with ME. That sounds more like a fuel delivery issue. Clogged filter, bad injector(s), weak pump, something of that sort.

Do you have the means to check the fuel pressure?

 

No, I don't yet. It's like a smooth than rough thing. Smooth half way through the cycle then rough, you can hear/feel it. The more RPM, the rougher it gets. The car has a fresh tune up including fuel filter. The fuel pump seems like its working properly. Could the lousy chip have something to do with it?

I mean I put a HyperTech chip is my 2.8 years ago not knowing any better and it wouldn't even start because of it. Put the stock chip back in and it was fine, got my money back too.

 

BTW, if you hold it at about 2000 RPM it is not just smooth revving. It'll be rough for a few sec then smooth, and will repeat that over and over again as you hold it there.

 

Smooth then rough...is this like a several second interval between? Or are we talking rapid... Rapid could be a down cylinder...if it's any decent amount of time for the rpms indicated then I'm thinking something else....

Sounds just like a stumble/surge to me though, not really a misfire.

Like they said, check your vacuum. Vacuum leak is a STRONG possibility for a stumble.

 

You should find somone with a fuel pressure gage around you. If it was a fuel delivery problem though, it would probably lose alot of power when this happens.


I would clean the Iac (for the hell of it), check for vacum leaks, get a fuel pressure gage, and get a compression tester. Mine as well cover all areas.

 

IMO, it feels like a slight shake coming from the engine for some reason. It's there at idle but you can really feel it when I rev and keep it at say 2000RPM and -- represents smoothness and << is roughness. Over the course of about 4 seconds it's like this:

-------<<<<--------<<<< and so on, over and over again.

So far I've heard and considered the coil, vaccum leaks, (which I doubt) HyperTech chip, (which I doubt) fuel injectors, and something in the trans.

 

Wires are brand new and it was doing it before I replaced them.

 

The first impression is usually the best. It's been said that you never forget your first one.

About all I can add to that would be purely instructional, so here goes:

Start by performing a power balance test, both for the ignition and injection systems. You'll need a handheld tachometer (you cannot use the dash gauge since it will be at best inaccurate, and at worst, grossly inaccurate), some simple tools, a notepad and writing instrument (in my case, a crayon is all I'm allowed) and probably a pair of spark plug boot pliers - the heavily insulated type so you don't stutter on the keyboard in your reply.

OBSERVATION: Why are pliers, scissors, or even pants sold in pairs? Ever walk into your favourite hardware store and ask for a single plier? Or scissor? Maybe there should be a Half-Gap that can sell a pant...

But I digress.

Get the engine running and warmed to operating temperature. Connect your tachometer, DMM, and set up as if you were going to set the TPS and minimum air position - because that's what you are going to do. In other words, disconnect the EST bypass connector, and disconnect the ISC stepper motor. If everything is correctly adjusted, the engine should idle, although at an RPM point much lower than normal. Just for grins, set the minimum air position to 500-550 RPM, then set the TPS to spec.

You'll need to continue your tests in this mode, since the ECM would otherwise try to adjust timing and ISC steps to compensate for RPM drops during the testing, rendering the results useless.

Once you're all set, make a note of the idle RPM. Disconnect the spark plug wire for the #1 cylinder. You can do that at either end, and I find it easier to do at the distributor end. Observe the drop in engine RPM. Record the reading. Reconnect the wire. Perform this same test for the remaining 7 cylinders in whatever order you desire - numerical, backward, firing order, lowest order prime numbers first, whatever.

Once you have all the readings, there may be a cylinder or two that had no change, or less of a change than the other cylinders. Those would be your prime suspects. Make a note of that, too.

Now you can disconnect the injector connector for each of the cylinders, one at a time, and in the same order. Again, allow about 15-20 seconds for everything to stabilize. This is even more important with the injectors, in case one is streaming, leaking, or otherwise flooding a port with fuel. You'll want to observe whether the RPM drop occurs immediately, or after a delay (indicating a leaker). Make a note of that, too.

Once you have all the RPM drop data, reconnect all your systems and remove your instruments. It would be interesting for us to see the results.

Oh, another thing - I'd like a pay increase. Make a note of that, too - In crayon, of course.

 

I had the same problem and got fixed when tuned the distributor up. Even when you said the car got fresh tuned up, check the distributor again.