High idle, high exhaust temp (Page 1/2)
84-barn_fresh JAN 25, 10:01 AM
84 4cyl sat for a long time one original owner 70k. Trying to get this thing running for my kid. Will start runs clean but idles high. New AIC same result. Stuffed a rag in the AIC hole and get the idle down to 1k. Will run clean for a min, then something changes and it will start running rough. Exhaust seems to be getting really hot really quick. New tstat. Cyl pressures from drivers side to passenger side, 140,110,140,140. Do I have a head gasket leak causing it to run lean? I have seen a small amount of smoke escaping between the head and block right by the large vac diaphragm in the center. Also the head seems to be baking the grease off of it right in the center on either side of the head.

Any help would be greatly appreciated

Edit: EGR valve is frozen solid. Took valve cover off, dirty but nothing looks terrible. EGR gasket looked good, tbi gasket looked good. Question would the stuck egr causes the high idle and high heat? Looks like it was stuck closed, pintle/diaphragm all the way out.

[This message has been edited by 84-barn_fresh (edited 01-28-2023).]

theogre JAN 25, 11:26 AM
High Idle and/or Lean is often a Vac Leak somewhere.

"I have seen a small amount of smoke escaping between the head and block right by the large vac diaphragm in the center."
Sound like EGR valve bad or have problems that can cause a vac leak.

See my Cave, Vac Leaks
can be iffy TBI or Intake parts or gaskets too.

Cyl pressures 140,110,140,140 isn't good but won't cause engine to run lean.
140 is a bit low. 110 is way low and "out of spec." If anything O2 often see Rich and may trip DTC 45 because low pressure often isn't burning fuel right.
In most cases w/ old engines you want highest and lowest to be 20psi difference max But Closer is much better.

110 can be many things... iffy head gasket, iffy valves or parts to run the valves, iffy Piston Rings, etc.
Cheap bore scope may help finding why 110. Example: Maybe Scratch bore you see using this thru spark plug hole. If true, engine is "dead."

⚠️ Warning: running lean can fry pistons and more. the Catalyst hate Rich and Lean and can overheat destroying itself and/or start a fire. Cat also gets Poison by "burning" oil, coolant, wrong sealers, etc. causing same results.

If valve cover is leaking or removed for any reason... use Fel-pro VS50179T PermaDryPlus valve cover gasket w/ new bolts etc. see https://www.fiero.nl/forum/Forum2/HTML/146650.html
Note: Come w/ new EGR gasket too so can reused old EGR if is good.
EGR bad... See my Cave, Emissions
84-barn_fresh JAN 25, 11:55 AM
Ogre really appreciate the reply. I suspect original owner had some overheating issues because the t-stat was removed. That scares me a bit but hopefully being an iron head it isn't warped or cracked. With the one cylinder at 110 sounds like I might as well take the head off don't you think? When exhaust was getting hot i originally thought clogged cat. So when I had the exhaust off to change the start I took care of that. The "cat" was already void of all the catalyst material but I cut all the baffles out because I thought they might be clogged, and welded it back up.
Dukesterpro JAN 25, 12:10 PM
I'm not an expert but I want to chime in here.


Before you go ripping the head off. Humor me. Pull your EGR, Pull your valve cover. Disconnect your coil to distributor lightening tube. have your kid roll the motor over while you watch the rocker arms. Make sure the rocker arms on your sleepy cylinder are moving the same amount as the rest of them. Mine had a sleepy cylinder too that I wrote off as rings way too early. Lifter started ticking and forced my hand into just slapping new flat tappets on there. Low and behold my low compression cylinder went away when I fixed the dead lifters. Unlikely fix, but might as well check.

Ogre is right that 140 is not exactly ideal. But I want to add on that if the old girl hasn't run in a while rings could be stuck or gummed up, once you get her running you might see some compression come back.

Also, check your timing. Significantly retarded timing can cause excessive exhaust temps. Check all of your vacuum lines. On my 84 there are 4 and a cap.

Good luck and don't forget to keep us updated, your forums posts create a valuable resource for future Fiero innocent victims, ahem, I mean eager enthusiasts.
84-barn_fresh JAN 25, 12:23 PM
Duke thank you for the reply, that is what I was thinking after you and orge's advice pull egr and pull valve cover before I go ripping the head off. I have replaced a few vac lines, going to get a hand vac pump today and test others. I could not tell if the smoke was escaping from the head or the egr as it is coming out right between the two. Would be great if it is just the egr gasket and maybe a stuck lifter. Crossing my fingers I don't really have the money to replace the head if its cracked or the engine if it's toast. My kid spent his hard earned money working with me last summer so hoping I can get it running. I have a bunch of other small issues to deal with and the engine has been slowing me down on finishing the rest.
84-barn_fresh FEB 21, 02:34 PM
Update

Took the entire top end apart. EGR was frozen solid and tstat was missing. I think this contributed to the sludge and the pcv passage under the throttle body to be completely clogged as well. Meticulously cleaned everything, cylinders looked ok, head and valves looked ok, all new gaskets, new tstat, new egr, new aic, new plugs wires cap and rotor, new starter, replaced vac lines, capped off brake booster line at intake for now. Replaced alternator while it was apart.

Idle is still wild but not as high as before, when it gets near 1k it gets rough then smooths out and likes to stay around 14-1500. Sounds clean and smooth when revving. Started knocking a bit once temps came up Exhaust and head still seems to be getting too hot. Oil pressure warning light not on. Changed oil, pulled t-stat. I am lost and frustrated my kids birthday is next week and I am not confident I can get it road worthy at all. Pulled rad cap briefly when first started and coolant started coming out the tstat housing so i think they water pump is working. Not sure why it is getting so hot. Confident the coolant passages in the head and intake are clear. With t-stat in temp took a normal amount of time to get up to around 200 then I watched it drop rapidly back down to 160 ish when the t-stat opened.

Its doing the exact same thing that it was before I took it apart. The middle two cylinders are heating up the exhaust red hot in less than two minutes. Outer two pipes are not nearly as hot. If I do not have a vacuum leak what else would cause that?

[This message has been edited by 84-barn_fresh (edited 02-21-2023).]

Dukesterpro FEB 21, 05:37 PM
Alright, lets take a breath and sort this out.

You and I are in the same high idle boat.
I'm going to assume you are not seeing any suspicious smoke from the exhaust pipe, so we can assume that your reassembly was good.


You mentioned is started knocking when temps came up. It may be your problem. Have you set ignition timing? Should be 8 degrees BTDC. You have to short teminals A and B on the ALDL connector in the center console when you make the adjustments.

In fact. Let it warm up and then short the terminal and see if the idle comes down. Shorting the terminal removes all electronic advance.
theogre FEB 21, 06:11 PM
you replace the head gasket?
Did you get new Head Bolts?

OE ones often have problems and break.

If you get new bolts now, change 1 bolt at a time to save the head gasket.
84-barn_fresh FEB 21, 06:14 PM
Thanks Duke I am just assuming the old guy that I bought it from did not mess with the timing but it sounds like that is the next logical step. Can I check it without shorting the ALDL terminals or is that a must?

thank you for the quick reply. Heading out to go work on his sisters Fusion door handle for the fourth time. Some times I really do not enjoy working on cars ;(
84-barn_fresh FEB 21, 08:26 PM
sorry for the double post I cant find the delete button#!

[This message has been edited by 84-barn_fresh (edited 02-21-2023).]