My girlfriend bought an '87 IROC-Z this past weekend and the old owner told us that the RPM's flutter between 40-70mph. I've been driving it since she bought it and sure enough, the car shakes slightly and the tach bounces when you're at cruising speeds. The old owner also said that he believed the original owner de-screened the MAF. Do '87s even have a MAF? If so, would that be the cause for this? I figured it's got to be an intake issue, I don't think it would be a fuel issue since it's got a LOT of pep from stop light to stop light. Any input would be great.

 

I seriously doubt that the MAF screens have anything to do with it. You might need a good tune up with new plugs and wires. I would guess something in the ignition system that is why the suggestion for plugs and wires.

 

Supposedly the plugs have been changed about 2 yrs ago. And I know what a car feels like when even ONE plug is bad. The '90 has a single plug that has gone bad and the difference between both cars is night and day?

 

if your tach is bouncing and the cars engine isnt bouncing with the tach then its an electronic issue, somewher between the distributor and the gage. the sputtering, i might wanna check timing, then the TPS, maybe its out of spec.

 

The engine DOES flutter with the tach. It jumps up/down usually between 250-300RPM. So I want to check the timing and throttle possitioning sensor? Anything else that might be out of whack?

 

it could be the EGR system, but timing and TPS sensor is the best thing to check out at this point.

it doesnt suddenly lose power at those rpms does it, that could be a fuel problem or a clogged cat.

 

No it doesn't lose power, it just flutters slightly. The old owner daily drove the car on a 60mile commute to and from work, it's nothing MAJOR. It's just an annoyance really.

 

mayb its an ignition problem, like theres a short in the coil or the wiring to the distributor? mayb the coil is gonna die. this is a real pickle here, let us know what u found, if anything.

 

I have the identical problem with my 86, carbed LG4. At cruising throttle positions, ie light throttle, under 2700rpm, I get the flutter in the tach from 250-500rpm, and I can feel it, pretty strong some times too. Its defitnetely in my ignition, and its not a single cylinder skip, its like the distributor is not being feed consistant power. As soon as I put my foot in it, or the rpms are over 2700rpm, the problem disapears completely. All the power it should have, pulls hard through the redline, etc. Starts nice and easy too. So, if you find out anything, let me know, cause I'm going to be chasing this down once the car comes out of storage this spring. I will of course do the same if I figure anything out.

I don't think it would be a throttle position sensor, or timing issue, the tps could cause some driveability problems, but reduced or advanced timing wouldn't cause the conditions we experience. I'm still thinking its power to the distributor cutting in and out, explaining the jump in the tach, which is larger than the jump in rpms the engine in acutally changing. If your riding a along, and the torque converter is locked up, there is no way the engine is jumping rpm that much, you'd be slamming around if that was the case, its just the signal going to the tach disapearing, or so I think.

 

maybe I'll replace the distributor and the coil and see if it fixes the problem

 

Just covering the basics here. You did check the PCV valve, the vacuum lines and the plug wires to make sure they don't have any minor splits that would allow the spark to ground out on the manifold, right? And you also checked the wiring for the tach itself to make sure it wasn't rotted or loose.

 

Any updates on this problem you were having, I'm still having the same trouble, haven't located the problem yet.

 

I had the same problem, started out only at certain RPMs then graduated to nearly all RPMs. Turned out to be badly worn connections in the distributor cap.

 

i had this issue before. i never did figure out what was wrong though. it happened around 70 mph on the highway during the winter. I also had the heat on when this occured. I havent noticed it much as of late since I havent been on the highway as much as i used to. I had a check engine light come on since and i had it checked out, apparently i had some wires unattached and it was not firing on all cylinders.

 

I have had a similar problem with my 88.

Do the RPM's drop or increase from the steady value the engine should be at?

I had an issue where the tach was grounding out and shorting the coil. It would make the car stumble and the tach would drop like a rock. The funny thing is the coil never really died but the tach ground did kill like 4 distributor modules.

I know this reply is late but if it helps then it was worth it.

Let me know

 

I got an 87' iroc-z and its got a maf right under the intake, 87's also have the screen you are talking about its easy to check if you have the screen, take off the huge plastic part of your intake covering your air filter(s) and look the in the hole, the screen should be right in front.