Hey, I'm new to diesels and went to look at one on a dealer lot. It's an '04 quad cab long bed 4x4 with 91,000 miles. It started with no problem but soon after, it had a quick surge of about 150-200 rpm and then idled somewhat rough, then returned to normal. It repeated this every 20-30 seconds or so and continued to do this for the entire time it was running, which was about 10 to 15 minutes. It seemed to disappear when I pressed the accelerator while it was in park. It was around 55-60* outside and had a nearly empty tank. It also had a squeel from a belt or pulley which increased slightly with engine speed. It already had the standard oil change service and cleaning at the dealer but the salesman said he would take it back to service in the morning. Any ideas what could be causing this or anything I should be wary of? I put this in urgent as I may have to put a deposit on it today as there were a few people there looking at it. Thanks.