Real Fiero Tech

So, when my car's at operating temp, idling around 1050 rpms. occasionally the engine light comes on (Idle speed error) and the idle goes up to 1100 rpm, but if I let it idle for a couple minutes or get on the accelerator the light goes off. My IAC was under warranty so I swapped it out and cleaned out the passage with some b12 chemtool, but the problem continues.......

any thoughts?

Start looking for vacuum leaks. It's a small one if the idle is only up 100-200 RPM. Start checking all those vacuum lines.

Fastback86 wrote:Start looking for vacuum leaks. It's a small one if the idle is only up 100-200 RPM. Start checking all those vacuum lines.

:thumbleft: yup. likely spots are the EGR tube & the brake booster - but, there are a few others too.

Egr tube is new-ish, and the last time I had it apart I cleaned out the passage in the intake with a 12ga bore brush on a power drill. I know I broke 1 vac line when I was messing with the tb coolant lines, but I patched it with a piece of rubber line. I'm gonna dig up my spare vac line set and pull the intake today, see what happens.

alright, I found my spare set of vac lines, cleaned and inspected them, and they looked good. I pulled the plenum, pulled the vac lines that were on the car, and there were a couple iffy things. the boot around the pcv was a little stretched out, and the rubber hose between the lower intake and the tb "heat riser" was as loose as a times square hooker. So I replaced the lines with the ones i cleaned, used a better pcv boot, and replaced the loose hose.
on further inspection the 1" long hose between the egr valve position sensor and the t fitting on the line from the egr was broken in half. obviously this was a problem, but i thought i would have gotten a egr position error code from that line being broken.

anyway, no engine light now, but now idling at 1100 steady with a little "hiccup" and idle surge every 15 to 20 seconds.....

I've been saying pics for a while so here's some...



ninja edit: i know everything's filthy but it's supposed to monsoon here for the next 3 days so no point in cleaning while things were apart.

Idling at 1100 cold or hot? Cold is right on, but if it doesn't drop to about 900 after it warms up, you've still got a problem

Fastback86 wrote:Idling at 1100 cold or hot? Cold is right on, but if it doesn't drop to about 900 after it warms up, you've still got a problem

Maybe his coolant temp sensor is bad

Or the Tach is off.

Should get a check engine light with a sustained high idle.

Series8217 wrote:

Fastback86 wrote:Idling at 1100 cold or hot? Cold is right on, but if it doesn't drop to about 900 after it warms up, you've still got a problem

Maybe his coolant temp sensor is bad

Could be. A scan tool would definitely help.

idles at 1500 to 2k surge at start, as soon as the temp gauge starts to climb idle is now usually hovering just above 1k with an occasional blip to 1100. also started hesitating today even when hot at 60 in 4th on the highway.
pulled the plugs, all were lightly coated white, replaced with a new set of #1 rapidfires
recently replaced:
tps iac and map tstat 195 (cold new england winter)
every coolant sensor except the cold start switch (temp gauge wiring swapped in the dash cluster and needle recalibrated using the how to from fierosails.com)
lemon? :dontknow:
can borrow realtime scantool, and i should to check the tach.
i'm pretty sure i heard a hiss when i pulled the plenum yesterday, but it went away pretty soon after i pulled it. i'm gonna loosen the plenum tomorrow and do a leak down test on the fuel system so i can listen for a leaky injector.

Well, I definitely missed a vacuum leak I can hear a hiss from the passenger side of the car while I'm driving. Plugs are also already lightly coated white again (only 2 weeks on a new set) so I'm running lean too. I'm off friday so I'm gonna pull the intake again, recheck all the vac lines, attempt to check the fuel reg diaphragm (#15? #17? torx security?- gotta try to get one)
and I think while I'm at it I'm gonna remove the pre-recall emission tube that connected the valve cover to the air filter, I'm gonna replace the steel vac line connected to it with a piece of brake line. they're both rusty as hell.

Take a piece of hose, stick one end in your ear and use the other as a probe to find the vacuum leak while the car's running. It's hard as hell to find a hissing noise on a car that can't run because it's taken apart.

well I ripped out the rusty lines on the firewall and replaced the vac line from the air filter to the evap solenoid with some new rubber hose and a piece of 1/4" brake line. Idle is now hovering between 950 and 1k. I can get the idle to drop to 900 by moving the hard line between the front valve cover and intake tube, so i ordered a set of pcv grommets from the fiero store. hopefully this is the final step in this cure. figure i shaved a pound or 2 off the car in the process by getting rid of that 1" wide unused pipe.

well, tach says car now idles between 900 and 950. no engine light.
among other issues, my #6 injector was clogged and #2 and my cold start were leaking. GP Sorenson sucks; those injectors were just over a year old.
I ended up buying a set of flow matched stock Densos for the 3.4 off of fiveomotorsport.com. $272 shipped, not bad. Between the injectors, valve cover grommets, and removing the cold start components I made good progress this week.

I did end up borrowing a real time scan tool and taking a ride around town. According to the scanner when my tach says 950 i'm idling at 1030, and the higher the RPM the more it's off. 2500 on the tach, the tool says 2650 and so on. Not surprisingly everything the tool will read is off by some margin, even my "recalibrated" coolant temp gauge is 20 deg higher than the tool said.

Is this just something I'm gonna have to live with? Is the tach being off like that a symptom of a failing tach filter, or a failing tach?

the tach was probably never perfectly accurate to begin with. its 80's technology man. I don't think being 100 or so rpm off is such a bad thing. Mine is off too as I have a digital tach gauge and mine is off around 150 at idle. I don't worry about it. nothing you can do really other then getting an aftermarket tach. Is it worth it though?

Changing the dash completely is in my plans for the distant future. It can wait till then.