I need help with a stumbling/idle problem

[pantera1683]

Okay, for the past month or so I have been having an intermittent problem with the Z stumbling while cruising. I first noticed it while driving at constant highway speed on a trip from Dallas to Houston. It would stumble or "hiccup" for a few seconds at a time as if it wasn't getting enough fuel. It did this for about 1/2 an hour and went away. I pulled the plenum and changed the alternator, coils and wires. I checked all the vacuum hoses and added zip ties to the connections. The hiccups would pop up very rarely after that.

On Vets day I got caught in a downpour and the stumbling came back, but this time it had a hard time accelerating from a stop. It struggled to accelerate until I stabbed the gas pedal, then it would accelerate normally. I pulled over and it shut off. It did start back up immediately after and seemed to work fine after. Yesterday, it was driving fine until I got a block from home, the stumble came back coming trying to accelerate from a stop and the idle went to 1200 rpm and kept rising to 2000 rpm.

Here is some background on the car. It is a 94 with 36k miles on it. It sat for several years before I purchased it earlier this year. I bought it with 33,5k miles and the PO only put 2k miles on it in the preceding 2 years. The fuel filter and plugs were all changed earlier this year.

Any ideas?

[sammy]

you might ck the sensor that on the rear of the manifold (map sensor )to see if the vacume connection is either full of oil or if it has just a rubber hose that connects it if the hose has gotten soft and is collapsing .also there is a map sensor right under the computor in the engine compartment thats partof the the secondary system . are you getting a ck engine light . do you have a scann tool to ck for codes . other things that could be causing it are your tps ,might have developed a flat spot . or the iac may have started to go south . does your secondary vac pump go on and stay shut off when you turn the key to on (but dont start it ) or does it cycle on every couple of seconds ????if it does you still have a vac leak.

[XfireZ51]

How does it idle? Any surge?

[pantera1683]

Idles smoothly, the MAP hose is new and clamped secure. The vac pump cycles every 5 seconds with key on engine off.

[XfireZ51]

Originally Posted by pantera1683

Idles smoothly, the MAP hose is new and clamped secure. The vac pump cycles every 5 seconds with key on engine off.

Vacuum Leak. Check secondaries.

[Paul Workman]

Originally Posted by pantera1683

Idles smoothly, the MAP hose is new and clamped secure. The vac pump cycles every 5 seconds with key on engine off.

Vacuum "leak" in the secondaries, as Dom said. However, it is not severe. Furthermore, the secondary system vacuum leak will NOT be the source of your stumbling.

Do you have a scanner? I swear...The ZR-1 should come with one as standard equipment: not that they're trouble prone, but these cars are rare and not many shops have even seen a ZR-1. I got a scanner on a close-out sale, but I'd pay twice as much if I had to if I had to replace it!

That said, I'm gonna take a WAG and zero in on the TPS too, as I have a little spot on mine that I never notice if I sweep past it quickly. But, dawdle on the throttle opening, and I get a quick little stumble. It's on my radar, but not a priority item...yet.

P.

[pantera1683]

I don't think the vacuum leak is the source of the stumbling either. The secondaries are working fine. I did clean the IAC as it was kind of "sooty" and the idle went back to normal.

I need to get a scanner any recommendations on which one to get and where to get one?

Also, what's the best way to check the TPS?

Thanks

[XfireZ51]

Originally Posted by pantera1683

I don't think the vacuum leak is the source of the stumbling either. The secondaries are working fine. I did clean the IAC as it was kind of "sooty" and the idle went back to normal.

I need to get a scanner any recommendations on which one to get and where to get one?

Also, what's the best way to check the TPS?

Thanks

Not sure why the pump would continue cycling if there is no problem with secondary vacuum.

TPS reading is easily done with scan tool. Bit more difficult using DVM

[pantera1683]

Originally Posted by XfireZ51

Not sure why the pump would continue cycling if there is no problem with secondary vacuum.

TPS reading is easily done with scan tool. Bit more difficult using DVM

There is a leak, but from what I've read it's just a minor one and wouldn't cause my problems, but I will take your advice and narrow down the leak just in case.

[XfireZ51]

Originally Posted by pantera1683

There is a leak, but from what I've read it's just a minor one and wouldn't cause my problems, but I will take your advice and narrow down the leak just in case.

IMO, no such thing as a "minor vacuum leak".