4AGE: Idle jump?

[MR2ENC]

Hey, I'm new here.

I went to check out a 1985 MR2 and it turns out it's mostly problem free. There are a few things I'm worried about though.

-The engine jumps revs while idling. The engine will idle normally for about a minute and then will jump up about 150-200rpm higher every few seconds. The rise is rapid not slow like on some other cars that I've seen this problem with. I think it's probably just the timing or maybe it needs new spark plugs. Do you guys think a tune-up would fix this problem?

-There's a bit of rust on the suspension mounting bolt on the left rear strut tower.

Unfortunately the tire pressure was low because the car had been sitting, so I didn't get to drive it. I plan on test driving it sometime this week.

Thanks.

[lsgheero]

the idle issue is likely to be a vacuum issue. however a tuneup isnt bad... is the current owner willing todo a tuneup?

generally if I am skeptical about buying something I will ask the owner to fix problems before I will buy it.... if they want the sale bad enough you would be surprised what some owners will do. But its also a 20+ year old car and most people rarely properly maintain their cars if at all lol so expect problems regardless.

[lsgheero]

As an example a buddy of mine recently bought a chevy s10 extreme and he ended up getting a new hood, front end, etc from the owner as part of the deal to fix damages to the car but it wasnt originally part of the deal just stuff the owner did in order to make the sale.

[muffinman]

idle jumping could be air in the cooling system. check and see if it might have a possible coolant leak or maybe it was just not properly bled. what ever you do just don't drive too much without checking that out.

[MR2ENC]

Thanks for the replies guys. I've been searching around the site for possible causes for the issue and I found a few. Seems this problem is rather common.

[Jackstand Queen]

Finally a new member who actually reads old posts, does searches, and doesn't wait to be spoon fed answers.

You're on my "A" list MR2ENC.

[falcon021084]

Originally Posted by MR2ENC

Thanks for the replies guys. I've been searching around the site for possible causes for the issue and I found a few. Seems this problem is rather common.

yeah, i just went through that situation idle jumping or hunting or idle bouncing w.e they call it. i had head gasket blown, freeze plugs flew off and the WAX type idle air valve sticking in the fast position, my car didn't leak coolant it piss coolant it got to the point where the idle would stay at 2,000 rpms (stable) n the bastard would not move from there. it felt like it was possessed i don't think noone here has gotten their mr2 to that condition :L

i would say most likely u need to do a radiator flush and buy a new idle control air valve.

[mr2_mk1.5]

I've run into the idle bouncinging situation with gen 1's before, its strange because of seen some do it and some don't do it, but after screwing around with this and that I discovered that the coolant doesn't flow through the IAC(idle air control) valve mounted under the throttle body, apparently for some reason some mk1's go static pressure in the valve(the coolant heats up and cools down but doesn't flow and thats what causes the surge), I've never figured out why but I found if you pull the feed line(coolant) off of the valve and jam a nut into the line it creates a small restriction that gets coolant flowing through the valve. I hope this helps because I know how annoying that surge is especially when every decaled honda in the city thinks you wanna race.

[falcon021084]

Originally Posted by mr2_mk1.5

I've run into the idle bouncinging situation with gen 1's before, its strange because of seen some do it and some don't do it, but after screwing around with this and that I discovered that the coolant doesn't flow through the IAC(idle air control) valve mounted under the throttle body, apparently for some reason some mk1's go static pressure in the valve(the coolant heats up and cools down but doesn't flow and thats what causes the surge), I've never figured out why but I found if you pull the feed line(coolant) off of the valve and jam a nut into the line it creates a small restriction that gets coolant flowing through the valve. I hope this helps because I know how annoying that surge is especially when every decaled honda in the city thinks you wanna race.

LOL! on the racing part. how about at the light when a cop's next to you. got pulled over for the surged. yes sir.

i'm actually in the phase, getting little surges, eventho i got a new idle control valve it still does it, so u mean getting a nut size of the hose hmm . wow that actually might work.

[falcon021084]

Originally Posted by mr2_mk1.5

I've run into the idle bouncinging situation with gen 1's before, its strange because of seen some do it and some don't do it, but after screwing around with this and that I discovered that the coolant doesn't flow through the IAC(idle air control) valve mounted under the throttle body, apparently for some reason some mk1's go static pressure in the valve(the coolant heats up and cools down but doesn't flow and thats what causes the surge), I've never figured out why but I found if you pull the feed line(coolant) off of the valve and jam a nut into the line it creates a small restriction that gets coolant flowing through the valve. I hope this helps because I know how annoying that surge is especially when every decaled honda in the city thinks you wanna race.

LOL! on the racing part. how about at the light when a cop's next to you. got pulled over for the surged. yes sir.

i'm actually in the phase, getting little surges, eventho i got a new idle control valve it still does it, so u mean getting a nut size of the hose hmm . wow that actually might work.

[falcon021084]

sorry for the double post, internet lagged on me :L